fix(drawer): not restoring focus on close (#7668)

Currently the drawer restores focus on close after its closing animation is done and it contains the currently-focused element. This will always evaluate to false, because the sidenav gets a `visibility: hidden` which will blur any focused elements that it may have. With these changes the drawer will restore focus when the animation starts and it's still visible.

Author: crisbeto

src/lib/sidenav/drawer.ts

@@ -307,6 +307,7 @@ export class MatDrawer implements AfterContentInit, OnDestroy {
       this._animationState = this._enableAnimations ? 'open' : 'open-instant';
     } else {
       this._animationState = 'void';
+      this._restoreFocus();
     }
 
     if (this._focusTrap) {