67476 fix build analysis errors (cla: yes, f: cupertino, framework)

67477 Migrate some material tests to nnbd (cla: yes, f: material design, framework)

67478 [flutter_tools] remove deprecated flutter command (cla: yes, tool)

67479 fix dart docs for build (cla: yes)

67482 Migrate More Material Tests (cla: yes, f: material design, framework, waiting for tree to go green)

67485 [flutter_tools] remove globals from compile and devices (cla: yes, tool)

67493 [flutter_tools] support powershell style help request (cla: yes, tool)

67525 unnecessary null comparison (a: tests, cla: yes, f: material design, framework, waiting for tree to go green)