fix(material-experimental/slide-toggle): fix focus indictor position (#19551)

Author: andrewseguin

src/material-experimental/mdc-slide-toggle/slide-toggle.scss

@@ -23,6 +23,14 @@
     pointer-events: none;
   }
 
+  // The thumb-underlay element has `mat-mdc-focus-indicator` which sets
+  // a relative position. This element must have absolute positioning. This
+  // has increased specificity than the style set in MDC to guarantee that
+  // it will be absolutely positioned.
+  .mdc-switch__thumb-underlay {
+    position: absolute;
+  }
+
   // The MDC switch styles related to the hover state are intertwined with the MDC ripple styles.
   // We currently don't use the MDC ripple due to size concerns, therefore we need to add some
   // additional styles to restore the hover state.