test(material-experimental/mdc-slider): add server-side rendering test (#22650)

Resolves a TODO about setting up an SSR check. It seems like the function call is safe, because we don't initialize the MDC logic on the server.

Author: crisbeto

src/material-experimental/mdc-slider/slider.ts

@@ -989,8 +989,6 @@ class SliderAdapter implements MDCSliderAdapter {
     return this._delegate._getInput(thumbPosition)._isFocused();
   }
   getThumbKnobWidth = (thumbPosition: Thumb): number => {
-    // TODO(wagnermaciel): Check if this causes issues for SSR
-    // once the mdc-slider is added back to the kitchen sink SSR app.
     return this._delegate._getKnobElement(thumbPosition).getBoundingClientRect().width;
   }
   getThumbBoundingClientRect = (thumbPosition: Thumb): ClientRect => {

src/universal-app/kitchen-sink-mdc/kitchen-sink-mdc.html

@@ -104,6 +104,16 @@ <h2>MDC slide-toggle</h2>
 <mat-slide-toggle>with a label</mat-slide-toggle>
 
 <h2>MDC Slider</h2>
+<mat-slider>
+  <input matSliderThumb value="60">
+</mat-slider>
+<mat-slider>
+  <input matSliderThumb value="50" disabled>
+</mat-slider>
+<mat-slider min="200" max="500" step="100" discrete showTickMarks>
+  <input value="300" matSliderStartThumb>
+  <input value="400" matSliderEndThumb>
+</mat-slider>
 
 <h2>MDC Tabs</h2>