72746 Roll Plugins from b4466e7c7fea to c986058e301c (1 revision) (cla: yes, waiting for tree to go green)

72748 Exclude ARM from macOS builds (cla: yes, platform-mac, tool, waiting for tree to go green)

72754 [flutter_releases] Flutter Beta 1.25.0-8.2 Framework Cherrypicks (cla: yes, engine, framework, team, tool)

72755 Migrate some sample code to NNBD [2] (a: null-safety, cla: yes, d: api docs, d: examples, documentation, f: cupertino, framework, team, waiting for tree to go green)

72756 run framework unit tests on html backend (cla: yes, team, waiting for tree to go green)