feat(material/datepicker): Add aria-current="date" to the current date's cell

Author: ByzantineFailure

src/material/datepicker/calendar-body.html

@@ -49,6 +49,7 @@
       [attr.aria-label]="item.ariaLabel"
       [attr.aria-disabled]="!item.enabled || null"
       [attr.aria-selected]="_isSelected(item.compareValue)"
+      [attr.aria-current]="todayValue === item.compareValue ? 'date' : null"
       (click)="_cellClicked(item, $event)"
       [style.width]="_cellWidth"
       [style.paddingTop]="_cellPadding"

src/material/datepicker/calendar-body.spec.ts

@@ -55,6 +55,13 @@ describe('MatCalendarBody', () => {
       expect(todayCell.innerHTML.trim()).toBe('3');
     });
 
+    it('sets aria-current="date" on today', () => {
+      const todayCell = calendarBodyNativeElement.querySelector(
+	      '[aria-current="date"] .mat-calendar-body-today')!;
+      expect(todayCell).not.toBeNull();
+      expect(todayCell.innerHTML.trim()).toBe('3');
+    });
+
     it('highlights selected', () => {
       const selectedCell = calendarBodyNativeElement.querySelector('.mat-calendar-body-selected')!;
       expect(selectedCell).not.toBeNull();