fixup! refactor: make all event emitters readonly

Author: rafaelss95

src/material/core/datetime/date-adapter.ts

@@ -32,7 +32,7 @@ export const MAT_DATE_LOCALE_PROVIDER = {provide: MAT_DATE_LOCALE, useExisting:
 export abstract class DateAdapter<D> {
   /** The locale to use for all dates. */
   protected locale: any;
-  protected _localeChanges = new Subject<void>();
+  protected readonly _localeChanges = new Subject<void>();
 
   /** A stream that emits when the locale changes. */
   readonly localeChanges: Observable<void> = this._localeChanges;

tools/public_api_guard/cdk/stepper.d.ts

@@ -48,7 +48,7 @@ export declare class CdkStepLabel {
 }
 
 export declare class CdkStepper implements AfterContentInit, AfterViewInit, OnDestroy {
-    protected _destroyed: Subject<void>;
+    protected readonly _destroyed: Subject<void>;
     _groupId: number;
     protected _orientation: StepperOrientation;
     _stepHeader: QueryList<FocusableOption>;

tools/public_api_guard/material/menu.d.ts

@@ -18,8 +18,8 @@ export declare class _MatMenuBase implements AfterContentInit, MatMenuPanel<MatM
     backdropClass: string;
     get classList(): string;
     set classList(classes: string);
-    readonly close: EventEmitter<void | 'click' | 'keydown' | 'tab'>;
-    readonly closed: EventEmitter<void | 'click' | 'keydown' | 'tab'>;
+    readonly close: EventEmitter<void | "click" | "keydown" | "tab">;
+    readonly closed: EventEmitter<void | "click" | "keydown" | "tab">;
     direction: Direction;
     get hasBackdrop(): boolean | undefined;
     set hasBackdrop(value: boolean | undefined);