[LLC, Persistence] Add doc comments

Signed-off-by: Sahil Kumar <[email protected]>

packages/stream_chat_persistence/lib/src/entity/reactions.dart

@@ -1,19 +1,26 @@
 import 'package:moor/moor.dart';
 import 'package:stream_chat_persistence/src/converter/map_converter.dart';
 
+/// Represents a [Reactions] table in [MoorChatDatabase].
 @DataClassName('ReactionEntity')
 class Reactions extends Table {
+  /// The id of the user that sent the reaction
   TextColumn get userId => text()();
 
+  /// The messageId to which the reaction belongs
   TextColumn get messageId =>
       text().customConstraint('REFERENCES messages(id) ON DELETE CASCADE')();
 
+  /// The type of the reaction
   TextColumn get type => text()();
 
+  /// The DateTime on which the reaction is created
   DateTimeColumn get createdAt => dateTime()();
 
+  /// The score of the reaction (ie. number of reactions sent)
   IntColumn get score => integer().nullable()();
 
+  /// Reaction custom extraData
   TextColumn get extraData => text().nullable().map(MapConverter<Object>())();
 
   @override