fix(material/slider): aria-valuetext host binding should be onPush compatible (#29042)

`MatSlider` updates `_valuetext` without marking for check. The easiest
way to fix these types of issues when values are not part of the public
API is to switch them to signals.

(cherry picked from commit ce87e55)

Author: atscott

src/material/slider/slider-input.ts

@@ -20,6 +20,7 @@ import {
   numberAttribute,
   OnDestroy,
   Output,
+  signal,
 } from '@angular/core';
 import {ControlValueAccessor, FormControl, NG_VALUE_ACCESSOR} from '@angular/forms';
 import {Subject} from 'rxjs';
@@ -69,7 +70,7 @@ export const MAT_SLIDER_RANGE_THUMB_VALUE_ACCESSOR: any = {
   host: {
     'class': 'mdc-slider__input',
     'type': 'range',
-    '[attr.aria-valuetext]': '_valuetext',
+    '[attr.aria-valuetext]': '_valuetext()',
     '(change)': '_onChange()',
     '(input)': '_onInput()',
     // TODO(wagnermaciel): Consider using a global event listener instead.
@@ -211,7 +212,7 @@ export class MatSliderThumb implements _MatSliderThumb, OnDestroy, ControlValueA
   _hostElement: HTMLInputElement;
 
   /** The aria-valuetext string representation of the input's value. */
-  _valuetext: string;
+  _valuetext = signal('');
 
   /** The radius of a native html slider's knob. */
   _knobRadius: number = 8;

src/material/slider/slider-interface.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {InjectionToken, ChangeDetectorRef} from '@angular/core';
+import {InjectionToken, ChangeDetectorRef, WritableSignal} from '@angular/core';
 import {MatRipple, RippleGlobalOptions} from '@angular/material/core';
 
 /**
@@ -183,7 +183,7 @@ export interface _MatSliderThumb {
   _isFocused: boolean;
 
   /** The aria-valuetext string representation of the input's value. */
-  _valuetext: string;
+  _valuetext: WritableSignal<string>;
 
   /**
    * Indicates whether UI updates should be skipped.

src/material/slider/slider.ts

@@ -726,7 +726,7 @@ export class MatSlider implements AfterViewInit, OnDestroy, _MatSlider {
     const valuetext = this.displayWith(source.value);
 
     this._hasViewInitialized
-      ? (source._valuetext = valuetext)
+      ? source._valuetext.set(valuetext)
       : source._hostElement.setAttribute('aria-valuetext', valuetext);
 
     if (this.discrete) {

tools/public_api_guard/material/slider.md

@@ -19,6 +19,7 @@ import { QueryList } from '@angular/core';
 import { RippleGlobalOptions } from '@angular/material/core';
 import { Subject } from 'rxjs';
 import { ThemePalette } from '@angular/material/core';
+import { WritableSignal } from '@angular/core';
 
 // @public
 export class MatSlider implements AfterViewInit, OnDestroy, _MatSlider {
@@ -290,7 +291,7 @@ export class MatSliderThumb implements _MatSliderThumb, OnDestroy, ControlValueA
     get value(): number;
     set value(value: number);
     readonly valueChange: EventEmitter<number>;
-    _valuetext: string;
+    _valuetext: WritableSignal<string>;
     writeValue(value: any): void;
     // (undocumented)
     static ɵdir: i0.ɵɵDirectiveDeclaration<MatSliderThumb, "input[matSliderThumb]", ["matSliderThumb"], { "value": { "alias": "value"; "required": false; }; }, { "valueChange": "valueChange"; "dragStart": "dragStart"; "dragEnd": "dragEnd"; }, never, never, true, never>;