74847 Swap mockito import for test/fake (cla: yes, team, tool)

74848 Run tests in sound null safety mode for fuchsia_remote_debug_protocol (cla: yes, team, waiting for tree to go green)

74853 Migrate flutter_goldens to NNBD (a: null-safety, cla: yes, framework, team, waiting for tree to go green)

74856 driver nnbd (a: tests, cla: yes, framework, team)

74857 Migrate remaining examples to null-safety (cla: yes, d: examples, team, waiting for tree to go green)

74861 Migrate some dev/ things to null-safety (cla: yes, team, waiting for tree to go green)