18396 Add ocmock to iOS unit tests xcode project (cla: yes, waiting for tree to go green)

18397 Remove rapidjson from TextInputModel (cla: yes)

18398 Manual Dart roll to 95e11bc2d30f7c1b9c49a4fc97a44c4b32fe66d8 (cla: yes, waiting for tree to go green)

18400 add nullability annotations to ui/text.dart (cla: yes)

18404 release previous canvas when picture is not painted (cla: yes)

18405 Disable flow tests. (cla: yes)