fix(material-experimental/mdc-chips): fix changed after checked error when restoring focus to input (#24243)

Fixes that the MDC chip grid was causing a "changed after checked" error when the last chip is removed, if it is used together with `mat-autocomplete`. The problem is that the chip grid focuses the input when the last chip is removed which then opens the autocomplete panel, resulting in an error.

(cherry picked from commit c5cede8)

Author: crisbeto

src/material-experimental/mdc-chips/chip-grid.ts

@@ -353,7 +353,9 @@ export class MatChipGrid
     if (this._chips.length > 0) {
       this._keyManager.setFirstCellActive();
     } else {
-      this._focusInput();
+      // Delay until the next tick, because this can cause a "changed after checked"
+      // error if the input does something on focus (e.g. opens an autocomplete).
+      Promise.resolve().then(() => this._chipInput.focus());
     }
 
     this.stateChanges.next();
@@ -548,9 +550,4 @@ export class MatChipGrid
 
     this._lastDestroyedChipIndex = null;
   }
-
-  /** Focus input element. */
-  private _focusInput() {
-    this._chipInput.focus();
-  }
 }