fix(slide-toggle): thumb animation not working on mobile (#15236)

With cc8f871, we enabled the `grabbing` cursor if the thumb container is pressed. This accidentally broke animation for the thumb sometimes because the `:active`
pseudo class is added on tap/touch and now accidentally sets the thumb transition duration to `0ms`. Rather we should only set the thumb transition duration to `0ms` if the user started dragging the thumb (with a small threshold)

Fixes #15232

Author: devversion

src/lib/slide-toggle/slide-toggle.scss

@@ -113,11 +113,14 @@ $mat-slide-toggle-bar-track-width: $mat-slide-toggle-bar-width - $mat-slide-togg
 
   // Once the thumb container is being dragged around, we remove the transition duration to
   // make the drag feeling fast and not delayed.
-  &.mat-dragging, &:active {
-    @include cursor-grabbing;
+  &.mat-dragging {
     transition-duration: 0ms;
   }
 
+  &:active {
+    @include cursor-grabbing;
+  }
+
   ._mat-animation-noopable & {
     transition: none;
   }