chore(docs): hide value accessors from docs (#13453)

* Since we recently added logic for showing constants in the docs, we should avoid showing the value accessor constants which are actually just used kind-of internally.

src/lib/datepicker/datepicker-input.ts

@@ -36,14 +36,14 @@ import {Subscription} from 'rxjs';
 import {MatDatepicker} from './datepicker';
 import {createMissingDateImplError} from './datepicker-errors';
 
-
+/** @docs-private */
 export const MAT_DATEPICKER_VALUE_ACCESSOR: any = {
   provide: NG_VALUE_ACCESSOR,
   useExisting: forwardRef(() => MatDatepickerInput),
   multi: true
 };
 
-
+/** @docs-private */
 export const MAT_DATEPICKER_VALIDATORS: any = {
   provide: NG_VALIDATORS,
   useExisting: forwardRef(() => MatDatepickerInput),

src/lib/slide-toggle/slide-toggle.ts

@@ -49,6 +49,7 @@ import {
 // Increasing integer for generating unique ids for slide-toggle components.
 let nextUniqueId = 0;
 
+/** @docs-private */
 export const MAT_SLIDE_TOGGLE_VALUE_ACCESSOR: any = {
   provide: NG_VALUE_ACCESSOR,
   useExisting: forwardRef(() => MatSlideToggle),

src/lib/slider/slider.ts

@@ -70,6 +70,7 @@ const MIN_VALUE_ACTIVE_THUMB_GAP = 10;
 /**
  * Provider Expression that allows mat-slider to register as a ControlValueAccessor.
  * This allows it to support [(ngModel)] and [formControl].
+ * @docs-private
  */
 export const MAT_SLIDER_VALUE_ACCESSOR: any = {
   provide: NG_VALUE_ACCESSOR,