fix(material/slider): update VI when toggling discrete (#25985)

* fix(material/slider): update VI when toggling discrete

* Fixes an issue where the value indicator ui is not
  initialized when toggling discrete on

* fixup! fix(material/slider): update VI when toggling discrete

* fixup! fix(material/slider): update VI when toggling discrete

Author: wagnermaciel

src/material/slider/slider.ts

@@ -135,6 +135,7 @@ export class MatSlider
   }
   set discrete(v: BooleanInput) {
     this._discrete = coerceBooleanProperty(v);
+    this._updateValueIndicatorUIs();
   }
   private _discrete: boolean = false;
 
@@ -485,8 +486,7 @@ export class MatSlider
     eInput._updateStaticStyles();
     sInput._updateStaticStyles();
 
-    this._updateValueIndicatorUI(eInput);
-    this._updateValueIndicatorUI(sInput);
+    this._updateValueIndicatorUIs();
 
     this._hasViewInitialized = true;
 
@@ -773,6 +773,19 @@ export class MatSlider
     }
   }
 
+  /** Updates all value indicator UIs in the slider. */
+  private _updateValueIndicatorUIs(): void {
+    const eInput = this._getInput(_MatThumb.END);
+    const sInput = this._getInput(_MatThumb.START);
+
+    if (eInput) {
+      this._updateValueIndicatorUI(eInput);
+    }
+    if (sInput) {
+      this._updateValueIndicatorUI(sInput);
+    }
+  }
+
   // Update Tick Mark Track Width
   //
   // 1. Min, max, or step