Make it possible to leave channels

- In a chat, if the chat is an InBroadcast, and it's not a contact
  request, then the `Leave` menu option is shown with the translated
  stock string `menu_leave_channel` as its label.
- If the user clicks on it, the confirmation dialog has
  `menu_leave_channel` (rather than `menu_leave_group`) as its positive
  option.

Counterpart of chatmail/core#6984.

Author: Hocuri

src/main/java/org/thoughtcrime/securesms/ConversationActivity.java

@@ -59,6 +59,7 @@
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import androidx.annotation.StringRes;
 import androidx.appcompat.app.ActionBar;
 import androidx.appcompat.app.AlertDialog;
 import androidx.appcompat.widget.SearchView;
@@ -446,9 +447,10 @@ public boolean onPrepareOptionsMenu(Menu menu) {
     }
 
     if (isMultiUser()) {
-      if (dcChat.isEncrypted()
+      if (dcChat.isInBroadcast() && !dcChat.isContactRequest()) {
+        menu.findItem(R.id.menu_leave).setTitle(R.string.menu_leave_channel).setVisible(true);
+      } else if (dcChat.isEncrypted()
           && dcChat.canSend()
-          && !dcChat.isInBroadcast()
           && !dcChat.isOutBroadcast()
           && !dcChat.isMailingList()) {
         menu.findItem(R.id.menu_leave).setVisible(true);
@@ -625,9 +627,16 @@ private void handleProfile(boolean showApps) {
   }
 
   private void handleLeaveGroup() {
+    @StringRes int leaveLabel;
+    if (dcChat.isInBroadcast()) {
+      leaveLabel = R.string.menu_leave_channel;
+    } else {
+      leaveLabel = R.string.menu_leave_group;
+    }
+
     AlertDialog dialog = new AlertDialog.Builder(this)
       .setMessage(getString(R.string.ask_leave_group))
-      .setPositiveButton(R.string.menu_leave_group, (d, which) -> {
+      .setPositiveButton(leaveLabel, (d, which) -> {
         dcContext.removeContactFromChat(chatId, DcContact.DC_CONTACT_ID_SELF);
         Toast.makeText(this, getString(R.string.done), Toast.LENGTH_SHORT).show();
       })

src/main/res/values/strings.xml

@@ -270,6 +270,7 @@
     <string name="menu_unarchive_chat">Unarchive Chat</string>
     <string name="menu_add_attachment">Add Attachment</string>
     <string name="menu_leave_group">Leave Group</string>
+    <string name="menu_leave_channel">Leave Channel</string>
     <string name="menu_delete_chat">Delete Chat</string>
     <!-- Command to delete all messages in a chat. The chat itself will not be deleted but will be empty afterwards, so make sure to be different from "Delete Chat" here. "Clear" is a verb here, "Empty Chat" would also be fine (eg. in German "Chat leeren") -->
     <string name="clear_chat">Clear Chat</string>
@@ -390,7 +391,7 @@
     <string name="videochat_invitation_body">You are invited to a video chat, click %1$s to join.</string>
 
     <!-- get confirmations -->
-    <string name="ask_leave_group">Are you sure you want to leave this group?</string>
+    <string name="ask_leave_group">Are you sure you want to leave?</string>
     <plurals name="ask_delete_chat">
         <item quantity="one">Delete %d chat on all your devices?</item>
         <item quantity="other">Delete %d chats on all your devices?</item>
@@ -920,7 +921,7 @@
     <!-- %1$s will be replaced by name and address of the contact removed from the group, %2$s will be replaced by name and address of the contact who did the action -->
     <string name="remove_member_by_other">Member %1$s removed by %2$s.</string>
     <!-- "left" in the meaning of "exited" -->
-    <string name="group_left_by_you">You left the group.</string>
+    <string name="group_left_by_you">You left.</string>
     <!-- "left" in the meaning of "exited"; %1$s will be replaced by name and address of the contact leaving the group -->
     <string name="group_left_by_other">Group left by %1$s.</string>
     <string name="group_image_deleted_by_you">You deleted the group image.</string>