TW: update Scratch.canDownload, add Scratch.download

Author: GarboMuffin

types/scratch-vm-extension.d.ts

@@ -33,7 +33,8 @@ declare namespace Scratch {
   function canReadClipboard(): Promise<boolean>;
   function canNotify(): Promise<boolean>;
   function canEmbed(): Promise<boolean>;
-  function canDownload(name: string): Promise<boolean>;
+  function canDownload(url: string, name: string): Promise<boolean>;
+  function download(url: string, name: string): Promise<void>;
   namespace Cast {
     function toNumber(value: unknown): number;
     function toString(value: unknown): string;