fix(material/datepicker): prevent calendar from stealing away focus (#31128)

An earlier change added some logic to the calendar to re-focus the active date if an input requiring a full re-render changes which can potentially cause focus to be lost.

The problem with this is that if the calendar is used on its own, it might steal away focus even though the user wasn't interacting with it.

These changes add a check that focus is inside the calendar before attempting to recapture it.

Fixes #30635.

(cherry picked from commit 5397b38)

Author: crisbeto

src/material/datepicker/calendar.ts

@@ -13,6 +13,7 @@ import {
   ChangeDetectionStrategy,
   ChangeDetectorRef,
   Component,
+  ElementRef,
   EventEmitter,
   Input,
   OnChanges,
@@ -41,6 +42,7 @@ import {MAT_SINGLE_DATE_SELECTION_MODEL_PROVIDER, DateRange} from './date-select
 import {MatIconButton, MatButton} from '../button';
 import {_IdGenerator, CdkMonitorFocus} from '@angular/cdk/a11y';
 import {_CdkPrivateStyleLoader, _VisuallyHiddenLoader} from '@angular/cdk/private';
+import {_getFocusedElementPierceShadowDom} from '@angular/cdk/platform';
 
 /**
  * Possible views for the calendar.
@@ -241,6 +243,7 @@ export class MatCalendar<D> implements AfterContentInit, AfterViewChecked, OnDes
   private _dateAdapter = inject<DateAdapter<D>>(DateAdapter, {optional: true})!;
   private _dateFormats = inject<MatDateFormats>(MAT_DATE_FORMATS, {optional: true});
   private _changeDetectorRef = inject(ChangeDetectorRef);
+  private _elementRef = inject<ElementRef<HTMLElement>>(ElementRef);
 
   /** An input indicating the type of the header component, if set. */
   @Input() headerComponent: ComponentType<any>;
@@ -457,9 +460,12 @@ export class MatCalendar<D> implements AfterContentInit, AfterViewChecked, OnDes
       const view = this._getCurrentViewComponent();
 
       if (view) {
-        // Schedule focus to be moved to the active date since re-rendering
-        // can blur the active cell. See #29265.
-        this._moveFocusOnNextTick = true;
+        // Schedule focus to be moved to the active date since re-rendering can blur the active
+        // cell (see #29265), however don't do so if focus is outside of the calendar, because it
+        // can steal away the user's attention (see #30635).
+        if (this._elementRef.nativeElement.contains(_getFocusedElementPierceShadowDom())) {
+          this._moveFocusOnNextTick = true;
+        }
 
         // We need to `detectChanges` manually here, because the `minDate`, `maxDate` etc. are
         // passed down to the view via data bindings which won't be up-to-date when we call `_init`.