feat(dialog): add ariaLabelledBy config option (#14943)

Adds the ability to set the `aria-labelledby` of a dialog without mat-dialog-title.

tools/public_api_guard/lib/dialog.d.ts

@@ -57,6 +57,7 @@ export declare class MatDialogClose implements OnInit, OnChanges {
 export declare class MatDialogConfig<D = any> {
     ariaDescribedBy?: string | null;
     ariaLabel?: string | null;
+    ariaLabelledBy?: string | null;
     autoFocus?: boolean;
     backdropClass?: string;
     closeOnNavigation?: boolean;