84140 Migrate hybrid_android_views to null safety (team, cla: yes, a: null-safety, tech-debt)

84145 Migrate integration_tests/channels to null safety (team, framework, cla: yes, waiting for tree to go green, a: null-safety, tech-debt)

84148 Remove unused protobuf dependency (team, cla: yes, waiting for tree to go green)

84153 Migrate dartdoc to null safety (team, cla: yes, waiting for tree to go green, a: null-safety, tech-debt)

84154 Revert “Migrate android_semantics_testing to null safety (#84136)” (team, a: accessibility, cla: yes)