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/service-worker/config/config.d.ts

@@ -0,0 +1,46 @@
+export declare interface AssetGroup {
+    installMode?: 'prefetch' | 'lazy';
+    name: string;
+    resources: {
+        files?: Glob[];
+        urls?: Glob[];
+    };
+    updateMode?: 'prefetch' | 'lazy';
+}
+
+export declare interface Config {
+    appData?: {};
+    assetGroups?: AssetGroup[];
+    dataGroups?: DataGroup[];
+    index: string;
+    navigationUrls?: string[];
+}
+
+export declare interface DataGroup {
+    cacheConfig: {
+        maxSize: number;
+        maxAge: Duration;
+        timeout?: Duration;
+        strategy?: 'freshness' | 'performance';
+    };
+    name: string;
+    urls: Glob[];
+    version?: number;
+}
+
+export declare type Duration = string;
+
+export declare interface Filesystem {
+    hash(file: string): Promise<string>;
+    list(dir: string): Promise<string[]>;
+    read(file: string): Promise<string>;
+    write(file: string, contents: string): Promise<void>;
+}
+
+export declare class Generator {
+    readonly fs: Filesystem;
+    constructor(fs: Filesystem, baseHref: string);
+    process(config: Config): Promise<Object>;
+}
+
+export declare type Glob = string;