fix(animations): @internal must use JSDoc tags. (#24928)

This change fixes up several comments that accidentally used the JSDoc
tag @internal in regular block comments (`/*` instead of `/**`).

This prevents a problem with Closure Compiler that balks at `@` tags
occuring in regular block comments, because it assumes they were
intended to be tags for the compiler.

When occuring in `/**` JSDoc, tsickle escapes the tags, so they do not
cause problems.

PR Close #24928

packages/platform-browser/animations/src/animation_renderer.ts

@@ -74,7 +74,7 @@ export class AnimationRendererFactory implements RendererFactory2 {
     this.promise.then(() => { this._microtaskId++; });
   }
 
-  /* @internal */
+  /** @internal */
   scheduleListenerCallback(count: number, fn: (e: any) => any, data: any) {
     if (count >= 0 && count < this._microtaskId) {
       this._zone.run(() => fn(data));