refactor(material/datepicker): expose year view change detector ref (#21499)

(cherry picked from commit 74cd45a)

Author: MichaelJamesParsons

src/material/datepicker/year-view.ts

@@ -138,7 +138,7 @@ export class MatYearView<D> implements AfterContentInit, OnDestroy {
    */
   _selectedMonth: number | null;
 
-  constructor(private _changeDetectorRef: ChangeDetectorRef,
+  constructor(readonly _changeDetectorRef: ChangeDetectorRef,
               @Optional() @Inject(MAT_DATE_FORMATS) private _dateFormats: MatDateFormats,
               @Optional() public _dateAdapter: DateAdapter<D>,
               @Optional() private _dir?: Directionality) {

tools/public_api_guard/material/datepicker.d.ts

@@ -497,6 +497,7 @@ export declare class MatStartDate<D> extends _MatDateRangeInputBase<D> implement
 }
 
 export declare class MatYearView<D> implements AfterContentInit, OnDestroy {
+    readonly _changeDetectorRef: ChangeDetectorRef;
     _dateAdapter: DateAdapter<D>;
     _matCalendarBody: MatCalendarBody;
     _months: MatCalendarCell[][];