[cloud_firestore] it should be possible to set GetOptions for query.snapshots()

[KristianBalaj]

Description

Let's have a query like this:

var query = FirebaseFirestore.instance
        .collection(Constants.productsCollection)
        .orderBy('_name_sort')
        .limit(5);

if (lastDocument != null) {
  query = query.startAfterDocument(lastDocument);
}

It is possible to set GetOptions when using query.get() method.
The problem is that we cannot set the GetOptions when using query.snapshots().

In our current example we would like to set it only to Source.server so we would not take data in the cache into account.

It is doing anomalies and wrong results in the data when fetching from cache.

Current behaviour of .snapshots()

Let's have these documents displayed as tuples (name, is in cache).

(A, true),
(B, true),
(C, true),
(D, true),
(E, false),
(F, true)

When executing the previous query with .snapshots() in case of ordering by the name (first item in the tuple), the first snapshot that comes in is A, B, C, D, F. After that comes another snapshot that removes the F and adds the E.

This is bad because the correct result should be without the F and with E like this - A, B, C, D, E.

Proposed behaviour

It should be possible to set GetOptions in the .snapshots() just like in get([GetOptions options]), so in case of value Source.server the query would ignore the cache.

Current workaround

As the initial query we do the get() with Source.server and after that we listen for changes with the .snapshots().
This is not that convenient.

Or to disable caching all along is another possible solution.