82498 Replace testUsingContext with testWithoutContext in a few places (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

82882 Remove more mocks from error_handling_io_test (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

83137 Move globals.artifacts to globals_null_migrated, update imports (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

83147 Migrate build_system, exceptions, and source to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

83153 Migrate compile to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)