fix(material/datepicker): use aria-live over cdkAriaLive on period bu…

…tton

On the period button on the calendar, use `aria-live` over `cdkAriaLive`
because that seems to work better with VoiceOver. This fixes an issue
where VoiceOver did not announce the month after clicking the "Month
Month"/"Previous Month" buttons (angular#24397).

Fixes angular#24397

src/material/datepicker/calendar-header.html

@@ -3,7 +3,7 @@
     <button mat-button type="button" class="mat-calendar-period-button"
             (click)="currentPeriodClicked()" [attr.aria-label]="periodButtonLabel"
             [attr.aria-describedby]="_buttonDescriptionId"
-            cdkAriaLive="polite">
+            aria-live="polite">
       <span [attr.id]="_buttonDescriptionId">{{periodButtonText}}</span>
       <svg class="mat-calendar-arrow" [class.mat-calendar-invert]="calendar.currentView !== 'month'"
            viewBox="0 0 10 5" focusable="false">