67811 Fix typos in the [BottomNavigationBar] document (cla: yes, d: api docs, f: material design, framework, waiting for tree to go green)

67887 [NNBD] Migrate some Material tests to NNBD (cla: yes, f: material design, framework)

67900 Expose date symbols and patterns for en_US in framework (a: internationalization, cla: yes, f: material design, framework, team)

67919 [Material] Use primary color for selected rows and checkboxes in DataTable (cla: yes, f: material design, framework, waiting for tree to go green)

67926 Date Picker jumps back to initialDatePickerMode after day selection (cla: yes, f: material design, framework)