Fix _focused signal not firing stateChanges (#29944)

(cherry picked from commit 9d4fa8f)

src/components-examples/material/form-field/form-field-custom-control/form-field-custom-control-example.ts

@@ -173,6 +173,7 @@ export class MyTelInput implements ControlValueAccessor, MatFormFieldControl<MyT
       this._placeholder();
       this._required();
       this._disabled();
+      this._focused();
       // Propagate state changes.
       untracked(() => this.stateChanges.next());
     });