ci: move public-api goldens to goldens directory (#35768)

Moves the public api .d.ts files from tools/public_api_guard to
goldens/public-api.

Additionally, provides a README in the goldens directory and a script
assist in testing the current state of the repo against the goldens as
well as a command for accepting all changes to the goldens in a single
command.

PR Close #35768

goldens/public-api/animations/browser/testing/testing.d.ts

@@ -0,0 +1,34 @@
+export declare class MockAnimationDriver implements AnimationDriver {
+    animate(element: any, keyframes: {
+        [key: string]: string | number;
+    }[], duration: number, delay: number, easing: string, previousPlayers?: any[]): MockAnimationPlayer;
+    computeStyle(element: any, prop: string, defaultValue?: string): string;
+    containsElement(elm1: any, elm2: any): boolean;
+    matchesElement(element: any, selector: string): boolean;
+    query(element: any, selector: string, multi: boolean): any[];
+    validateStyleProperty(prop: string): boolean;
+    static log: AnimationPlayer[];
+}
+
+export declare class MockAnimationPlayer extends NoopAnimationPlayer {
+    currentSnapshot: ɵStyleData;
+    delay: number;
+    duration: number;
+    easing: string;
+    element: any;
+    keyframes: {
+        [key: string]: string | number;
+    }[];
+    previousPlayers: any[];
+    previousStyles: {
+        [key: string]: string | number;
+    };
+    constructor(element: any, keyframes: {
+        [key: string]: string | number;
+    }[], duration: number, delay: number, easing: string, previousPlayers: any[]);
+    beforeDestroy(): void;
+    destroy(): void;
+    finish(): void;
+    hasStarted(): boolean;
+    play(): void;
+}