92861 Remove globals_null_migrated.dart, move into globals.dart (a: text input, tool, cla: yes, waiting for tree to go green, integration_test, a: null-safety)

92869 Migrate build_system targets to null safety (tool, cla: yes, waiting for tree to go green, a: null-safety, tech-debt)

92871 Migrate flutter_command to null safety (tool, cla: yes, waiting for tree to go green, a: null-safety, tech-debt)

92952 Migrate doctor, format, and a few other commands to null safety (tool, cla: yes, waiting for tree to go green, a: null-safety, tech-debt)