70343 Code sample small fixes (adopt a widget, cla: yes, d: api docs, f: material design, framework, waiting for tree to go green)

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)

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