Revert "refactor(platform-browser): move platform-browser/animations to animations/browser (#15043)"

This reverts commit 195b863ea4.

tools/public_api_guard/platform-browser/typings/animations/index.d.ts

@@ -1,3 +1,11 @@
+/** @experimental */
+export declare abstract class AnimationDriver {
+    abstract animate(element: any, keyframes: {
+        [key: string]: string | number;
+    }[], duration: number, delay: number, easing: string, previousPlayers?: any[]): any;
+    static NOOP: AnimationDriver;
+}
+
 /** @experimental */
 export declare class BrowserAnimationsModule {
 }