76415 [devicelab] Separate build and test from Flutter gallery tests (a: accessibility, cla: yes, team, waiting for tree to go green)

76416 [flutter_tools] remove globals and mocks from android gradle builder and test (cla: yes, tool)

76420 Update all packages and upgrade to path_provider 2.0.0-nullsafety (cla: yes, team, tool)

76425 Remove unused flutter_driver_screenshot integration test (cla: yes, team, waiting for tree to go green)

76426 Remove unused ios_add2app integration test (cla: yes, team)

76429 Remove unused android_splash_screens integration test (cla: yes, team, waiting for tree to go green)

76430 Remove unused image_loading integration test (cla: yes, team)