92758 Improve error message for uninitialized channel (framework, cla: yes, waiting for tree to go green)

92808 feat: mirgate test_data/compile_error_project.dart to null safety (tool, cla: yes, waiting for tree to go green)

92812 migrate integration.shard/vmservice_integration_test.dart to null safety (tool, cla: yes, waiting for tree to go green, integration_test)

92822 Reland “Refactor ThemeData  (#91497)” (part 1) (framework, f: material design, cla: yes)

92849 Migrate tracing to null safety (tool, cla: yes, waiting for tree to go green, a: null-safety, tech-debt)