DOCSP-38015: Add new collection listener properties (#3252)

## Pull Request Info

Jira ticket: https://jira.mongodb.org/browse/DOCSP-38015

- [React to Changes - Flutter
SDK](https://preview-mongodbcbullinger.gatsbyjs.io/realm/docsp-38015-dart-react-to-changes-updates/sdk/flutter/realm-database/react-to-changes/):
Add new `isCleared` and `isCollectionDeleted` properties to list, set,
and map tabs

### Reminder Checklist

Before merging your PR, make sure to check a few things.

- [x] Did you tag pages appropriately?
  - genre
  - meta.keywords
  - meta.description
- [x] Describe your PR's changes in the Release Notes section
- [x] Create a Jira ticket for related docs-app-services work, if any

### Release Notes

- **Flutter** SDK
- Realm Database/React to Changes: Update "Register Collection Change
Listeners" section to document the `isCollectionDeleted` property for
list, set, and map collections and the `isCleared` property for map
collections.

### Review Guidelines


[REVIEWING.md](https://github.com/mongodb/docs-realm/blob/master/REVIEWING.md)

Author: cbullinger

examples/dart/test/react_to_changes_test.dart

@@ -2,7 +2,6 @@
 
 import 'package:test/test.dart';
 import 'package:realm_dart/realm.dart';
-import './utils.dart';
 part 'react_to_changes_test.realm.dart';
 
 // :snippet-start: sample-data-models
@@ -71,16 +70,16 @@ void main() {
       // Listen for changes on whole collection
       final characters = realm.all<Character>();
       final subscription = characters.changes.listen((changes) {
-        changes.inserted; // indexes of inserted objects
-        changes.modified; // indexes of modified objects
-        changes.deleted; // indexes of deleted objects
-        changes.newModified; // indexes of modified objects
-        // after deletions and insertions are accounted for
-        changes.moved; // indexes of moved objects
-        changes.results; // the full List of objects
+        changes.inserted; // Indexes of inserted objects.
+        changes.modified; // Indexes of modified objects.
+        changes.deleted; // Indexes of deleted objects.
+        changes.newModified; // Indexes of modified objects after accounting for deletions & insertions.
+        changes.moved; // Indexes of moved objects.
+        changes.results; // The full List of objects.
+        changes.isCleared; // `true` after call to characters.clear(); otherwise, `false`.
       });
 
-      // Listen for changes on RealmResults
+      // Listen for changes on RealmResults.
       final hobbits = fellowshipOfTheRing.members.query('species == "Hobbit"');
       final hobbitsSubscription = hobbits.changes.listen((changes) {
         // ... all the same data as above
@@ -89,7 +88,7 @@ void main() {
       await Future<void>.delayed(Duration(milliseconds: 10));
       // :snippet-start: pause-resume-subscription
       subscription.pause();
-      // the changes.listen() method won't fire until the subscription is resumed
+      // The changes.listen() method won't fire until subscription is resumed.
       subscription.resume();
       // :snippet-end:
       await Future<void>.delayed(Duration(milliseconds: 10));
@@ -103,9 +102,9 @@ void main() {
       final frodo = globalFrodo;
       // :snippet-start: realm-object-change-listener
       final frodoSubscription = frodo.changes.listen((changes) {
-        changes.isDeleted; // if the object has been deleted
-        changes.object; // the RealmObject being listened to, `frodo`
-        changes.properties; // the changed properties
+        changes.isDeleted; // If the object has been deleted.
+        changes.object; // The RealmObject being listened to, `frodo`.
+        changes.properties; // The changed properties.
       });
       // :snippet-end:
       await Future<void>.delayed(Duration(milliseconds: 10));
@@ -117,16 +116,14 @@ void main() {
       // :snippet-start: realm-list-change-listener
       final fellowshipSubscription =
           fellowshipOfTheRing.members.changes.listen((changes) {
-        changes.inserted; // indexes of inserted Realm objects
-        changes.modified; // indexes of modified Realm objects
-        changes.deleted; // indexes of deleted Realm objects
-        changes.newModified; // indexes of modified Realm objects
-        // after deletions and insertions are accounted for
-        changes.moved; // indexes of moved Realm objects
-        changes.list; // the full RealmList of Realm objects
-        // `true` after call to fellowshipOfTheRing.members.clear().
-        // Otherwise false.
-        changes.isCleared;
+        changes.inserted; // Indexes of inserted objects.
+        changes.modified; // Indexes of modified objects.
+        changes.deleted; // Indexes of deleted objects.
+        changes.newModified; // Indexes of modified objects after accounting for deletions & insertions.
+        changes.moved; // Indexes of moved objects.
+        changes.list; // The full RealmList of objects.
+        changes.isCleared; // `true` after call to fellowshipOfTheRing.members.clear(); otherwise, `false`.
+        changes.isCollectionDeleted; // `true` if the collection is deleted; otherwise, `false`.
       });
       // :snippet-end:
       await Future<void>.delayed(Duration(milliseconds: 10));

source/examples/generated/flutter/react_to_changes_test.snippet.pause-resume-subscription.dart

@@ -1,3 +1,3 @@
 subscription.pause();
-// the changes.listen() method won't fire until the subscription is resumed
+// The changes.listen() method won't fire until subscription is resumed.
 subscription.resume();

source/examples/generated/flutter/react_to_changes_test.snippet.query-change-listener.dart

@@ -1,16 +1,16 @@
 // Listen for changes on whole collection
 final characters = realm.all<Character>();
 final subscription = characters.changes.listen((changes) {
-  changes.inserted; // indexes of inserted objects
-  changes.modified; // indexes of modified objects
-  changes.deleted; // indexes of deleted objects
-  changes.newModified; // indexes of modified objects
-  // after deletions and insertions are accounted for
-  changes.moved; // indexes of moved objects
-  changes.results; // the full List of objects
+  changes.inserted; // Indexes of inserted objects.
+  changes.modified; // Indexes of modified objects.
+  changes.deleted; // Indexes of deleted objects.
+  changes.newModified; // Indexes of modified objects after accounting for deletions & insertions.
+  changes.moved; // Indexes of moved objects.
+  changes.results; // The full List of objects.
+  changes.isCleared; // `true` after call to characters.clear(); otherwise, `false`.
 });
 
-// Listen for changes on RealmResults
+// Listen for changes on RealmResults.
 final hobbits = fellowshipOfTheRing.members.query('species == "Hobbit"');
 final hobbitsSubscription = hobbits.changes.listen((changes) {
   // ... all the same data as above

source/examples/generated/flutter/react_to_changes_test.snippet.realm-list-change-listener.dart

@@ -1,13 +1,11 @@
 final fellowshipSubscription =
     fellowshipOfTheRing.members.changes.listen((changes) {
-  changes.inserted; // indexes of inserted Realm objects
-  changes.modified; // indexes of modified Realm objects
-  changes.deleted; // indexes of deleted Realm objects
-  changes.newModified; // indexes of modified Realm objects
-  // after deletions and insertions are accounted for
-  changes.moved; // indexes of moved Realm objects
-  changes.list; // the full RealmList of Realm objects
-  // `true` after call to fellowshipOfTheRing.members.clear().
-  // Otherwise false.
-  changes.isCleared;
+  changes.inserted; // Indexes of inserted objects.
+  changes.modified; // Indexes of modified objects.
+  changes.deleted; // Indexes of deleted objects.
+  changes.newModified; // Indexes of modified objects after accounting for deletions & insertions.
+  changes.moved; // Indexes of moved objects.
+  changes.list; // The full RealmList of objects.
+  changes.isCleared; // `true` after call to fellowshipOfTheRing.members.clear(); otherwise, `false`.
+  changes.isCollectionDeleted; // `true` if the collection is deleted; otherwise, `false`.
 });

source/examples/generated/flutter/react_to_changes_test.snippet.realm-object-change-listener.dart

@@ -1,5 +1,5 @@
 final frodoSubscription = frodo.changes.listen((changes) {
-  changes.isDeleted; // if the object has been deleted
-  changes.object; // the RealmObject being listened to, `frodo`
-  changes.properties; // the changed properties
+  changes.isDeleted; // If the object has been deleted.
+  changes.object; // The RealmObject being listened to, `frodo`.
+  changes.properties; // The changed properties.
 });