69594 Fix textfield messing with user-supplied input formatter list (cla: yes, f: cupertino, f: material design, framework, waiting for tree to go green)

69596 Updated the button.icon factory constructors for NNBD (cla: yes, f: material design, framework)

69610 Make header optional in PaginatedDataTable (cla: yes, f: material design, framework, waiting for tree to go green)

69614 Remove usage of –enable-experiment to analysis server (cla: yes, engine, framework, tool)

69617 Remove references to Window, and switch usages to PlatformDispatcher or SingletonFlutterWindow (a: accessibility, a: tests, cla: yes, f: material design, framework, team, tool)