74075 [flutter_tools] handle NPE in language analytics (cla: yes, tool, waiting for tree to go green)

74079 [flutter_tools] verify successful dart migrate (cla: yes, tool, waiting for tree to go green)

74090 Tests that module/plugin/package templates can be migrated to null-safety (cla: yes, tool, waiting for tree to go green)

74091 [flutter_tools] ensure allowExistingDdsInstance param is always non-null (cla: yes, tool)

74215 Use package:vm_service instead of json_rpc_2 (cla: yes, team, tool)

74249 [flutter_tools] ensure pub get can run from partially valid state (cla: yes, tool, waiting for tree to go green)