feat(storage): Add getDownloadUrl method to the Storage API

etc/firebase-admin.api.md

@@ -8,6 +8,8 @@
 
 import { Agent } from 'http';
 import { Bucket } from '@google-cloud/storage';
+import { File } from '@google-cloud/storage';
+import { FileOptions } from '@google-cloud/storage';
 import { FirebaseDatabase } from '@firebase/database-types';
 import * as _firestore from '@google-cloud/firestore';
 import * as rtdb from '@firebase/database-types';

etc/firebase-admin.storage.api.md

@@ -8,6 +8,8 @@
 
 import { Agent } from 'http';
 import { Bucket } from '@google-cloud/storage';
+import { File } from '@google-cloud/storage';
+import { FileOptions } from '@google-cloud/storage';
 
 // Warning: (ae-forgotten-export) The symbol "App" needs to be exported by the entry point index.d.ts
 //
@@ -17,7 +19,8 @@ export function getStorage(app?: App): Storage;
 // @public
 export class Storage {
     get app(): App;
-    bucket(name?: string): Bucket;
+    // Warning: (ae-forgotten-export) The symbol "FirebaseStorageBucket" needs to be exported by the entry point index.d.ts
+    bucket(name?: string): FirebaseStorageBucket;
 }
 
 ```