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

`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.

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) {