51680 [flutter_tools] update visual studio and validator to remove globals, update test cases (cla: yes, tool)

51684 [flutter_tools] no more MockLogger (cla: yes, tool, waiting for tree to go green)

51687 Write FLUTTER_BUILD_MODE when using a local engine (cla: yes, tool)

51689 Roll engine 96061d62281d..142882e1baea (9 commits) (cla: yes, waiting for tree to go green)

51693 Roll engine 142882e1baea..755e2b559d4d (4 commits) (cla: yes, waiting for tree to go green)

51714 [flutter_tools] Allow providing dart-defines to Android, iOS, macOS builds (cla: yes, team, tool)