feat(mat-calendar): Automatically reposition "close calendar" button if it is offscreen

### Feature Description

When using keyboard navigation, the "close calendar" button is placed at the bottom of the calendar after tabbing through the other interactive elements in the component. If this button would be positioned offscreen, it should be repositioned into view to improve accessibility.

### Use Case

A user may increase the browser size to 200%, or the calendar may just be positioned toward the bottom of the screen, which may cause this close button to render offscreen when displayed.

Start with the Angular Material calendar component and its keyboard-navigation behavior, focusing on how the close calendar button is placed after tabbing through interactive elements. Reproduce the case at 200% browser zoom or with the calendar near the bottom of the screen, then verify that the focused close button is repositioned into view.

Written by the indexing model from the issue text.