Show a prompt to reinvite other party in a DM

If you are looking at a DM where the other party has left then
when you focus the composer for the first time we'll show a
dialog asking if you want to reinvite the other party.

Closes #590

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/room/RustMatrixRoom.kt

@@ -174,6 +174,9 @@ class RustMatrixRoom(
     override val joinedMemberCount: Long
         get() = innerRoom.joinedMembersCount().toLong()
 
+    override val activeMemberCount: Long
+        get() = innerRoom.activeMembersCount().toLong()
+
     override suspend fun updateMembers(): Result<Unit> = withContext(coroutineDispatchers.io) {
         val currentState = _membersStateFlow.value
         val currentMembers = currentState.roomMembers()