test(material-experimental/mdc-slider): add tests for slider with set… (#22238)

* test(material-experimental/mdc-slider): add tests for slider with set displayWith

* fix(material-experimental/mdc-slider): trigger change detection when the value indicator text changes

Author: wagnermaciel

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

@@ -678,7 +678,7 @@ describe('MDC-based MatSlider' , () => {
     });
   });
 
-  describe('slider with custom thumb label formatting', () => {
+  describe('range slider with custom thumb label formatting', () => {
     let fixture: ComponentFixture<DiscreteRangeSliderWithDisplayWith>;
     let sliderInstance: MatSlider;
     let startValueIndicatorTextElement: Element;