83182 Add maskable icons to improve lighthouse score (team, tool, cla: yes, waiting for tree to go green)

83308 Pass –local-engine* from dev/bots/test.dart to pub test (only web) (team, cla: yes)

83310 Migrate localizations and generate_synthetic_packages to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

83311 Migrate deferred_components_gen_snapshot_validator to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

83313 [flutter_conductor] Migrate flutter conductor out of dev/tools and into its own directory (team, cla: yes)