84065 Migrate gallery test to null safety (team, a: accessibility, cla: yes, waiting for tree to go green, a: null-safety, tech-debt)

84066 migrate platform channels benchmarks (team, cla: yes, waiting for tree to go green, a: null-safety, tech-debt)

84125 Ignore unnecessary_import reports in sample code (team, cla: yes, waiting for tree to go green)

84130 Update dartdoc to 0.45.0 (team, cla: yes, waiting for tree to go green)

84136 Migrate android_semantics_testing to null safety (team, a: accessibility, cla: yes, waiting for tree to go green, a: null-safety, tech-debt)