66597 Replaced obsolete use of FlatButton with TextButton (cla: yes, f: material design, framework, waiting for tree to go green)

66602 Replaced obsolete use of FlatButton with TextButton in scroll_activity_test (cla: yes, framework)

66603 Replaced use of obsolete RaisedButton with ElevatedButton in widget_inspector_test (cla: yes, framework)

66633 migration of material files to nullsafety (cla: yes, f: material design, framework, waiting for tree to go green)

66639 Further explain parent constraints in SizedBox (cla: yes, d: api docs, documentation, framework, waiting for tree to go green)

66640 Add decoration parameter to DataTable and DataTableTheme (cla: yes, f: material design, framework)