build: fix build failure in latest MDC canary (#20597)

Fixes a build error due to a new required property.

(cherry picked from commit c21c6f5)

Author: crisbeto

package.json

@@ -61,7 +61,7 @@
     "@types/youtube": "^0.0.38",
     "@webcomponents/custom-elements": "^1.1.0",
     "core-js": "^2.6.9",
-    "material-components-web": "8.0.0-canary.fc0eb5013.0",
+    "material-components-web": "8.0.0-canary.3e435ba57.0",
     "rxjs": "^6.5.3",
     "rxjs-tslint-rules": "^4.33.1",
     "systemjs": "0.19.43",

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

@@ -257,7 +257,8 @@ export class MatSlider implements AfterViewInit, OnChanges, OnDestroy, ControlVa
     deregisterWindowEventHandler: () => {},
     removeTrackActiveStyleProperty: (_propertyName: string) => {},
     emitDragStartEvent: (_value: number, _thumb: Thumb) => {},
-    emitDragEndEvent: (_value: number, _thumb: Thumb) => {}
+    emitDragEndEvent: (_value: number, _thumb: Thumb) => {},
+    getValueToAriaValueTextFn: () => null
   };
 
   /** Instance of the MDC slider foundation for this slider. */