59184 [flutter_tools] remove globals from compilers (cla: yes, team, tool)

59209 Support .flutter-plugins-dependencies (cla: yes, platform-ios, team, tool, waiting for tree to go green)

59215 [flutter_tools] Update roll_dev.dart (cla: yes, team, tool, waiting for tree to go green)

59257 fix tree (cla: yes, team)

59267 Characters package (cla: yes, team, waiting for tree to go green)

59276 Add –device-id option for devicelab/bin/run.dart (cla: yes, team)

59280 test flutter framework with null-safety (cla: yes, d: examples, team, waiting for tree to go green)