65416 Re-land ScaffoldMessenger (cla: yes, f: material design, framework, waiting for tree to go green)

65426 [flutter_tools] remove advice about running sdkmanager directly in favor of directing to flutter.dev (cla: yes, tool, waiting for tree to go green)

65434 [devicelab] Remove ~/.gradle after each devicelab task run (cla: yes, team, waiting for tree to go green)

65435 [flutter_tools] alternate the name of the dill file used for hot restart (cla: yes, tool)

65460 Clarified ‘/’ route in initialRoute docs (cla: yes, framework, waiting for tree to go green)

65481 Remove mac prod builder. (cla: yes, team)