70368 [integration_test] Wrap pumped widgets with a RepaintBoundary (cla: yes, framework, waiting for tree to go green)

70379 Added Tabar Code samples (adopt a widget, cla: yes, d: api docs, d: examples, documentation, f: material design, framework, waiting for tree to go green)

70382 Update FlexibleSpaceBar dartpad sample (adopt a widget, cla: yes, d: api docs, d: examples, documentation, f: material design, framework, waiting for tree to go green)

70388 Revert “Roll Engine from c5c7e83b9e53 to d97a81c88983 (6 revisions)” (cla: yes, engine)

70391 Revert “Default Keyboard ScrollActions with PrimaryScrollController” (cla: yes, f: cupertino, f: material design, framework)