fix(material-experimental/mdc-form-field): avoid expression ch… (#18741)

There is currently a bug in the Angular Framework that results in
ExpressionChangedAfterItHasBeenChecked errors not throwing when they
should for OnPush components. Becuase we modify a variable used in the
template after it was already checked (in ngAfterViewInit), we need to
trigger change detection manually or the change might not be picked up.

src/material-experimental/mdc-form-field/form-field.ts

@@ -330,6 +330,9 @@ export class MatFormField implements AfterViewInit, OnDestroy, AfterContentCheck
     this._refreshOutlineNotchWidth();
     // Enable animations now. This ensures we don't animate on initial render.
     this._subscriptAnimationState = 'enter';
+    // Because the above changes a value used in the template after it was checked, we need
+    // to trigger CD or the change might not be reflected if there is no other CD scheduled.
+    this._changeDetectorRef.detectChanges();
   }
 
   ngAfterContentInit() {