72477 Updated the MaterialBanner example, NNBD, etc (cla: yes, f: material design, framework, waiting for tree to go green)

72488 Support flutter_test_config for flutter test on web platforms (cla: yes, framework, tool, waiting for tree to go green)

72490 Bottom navigation items length docs (cla: yes, d: api docs, f: material design, framework, waiting for tree to go green)

72494 Fix flutter in preparation for implementing Dart’s “Infer non-nullability from local boolean variables” (cla: yes, framework)

72512 fix a DragTarget type cast bug (cla: yes, framework, waiting for tree to go green)

72526 Make RenderColoredBox.paint() skip painting color if it’s transparent (cla: yes, framework, will affect goldens)