62367 Make dartdoc warnings fatal (& cleanup of warnings) (a: accessibility, a: internationalization, a: tests, cla: yes, f: cupertino, f: material design, framework, team, waiting for tree to go green)

62473 Fix ‘unresolved doc reference’ for material A-D (cla: yes, f: cupertino, f: material design, framework, waiting for tree to go green)

62741 Deprecate iOS13 style ActivityIndicator (cla: yes, f: cupertino, framework, waiting for tree to go green)

62755 Add punctuation for unterminated sentences in doc comments (a: accessibility, a: internationalization, a: tests, cla: yes, d: api docs, documentation, f: cupertino, f: material design, framework, tool)