[WasmFS] FS.readFile on main thread

When exporting and sharing files, we need to move the file into a File or a Blob object.

` const blob = new Blob( [FS.readFile( path )], { 'type': type } );`

With an asynchronous wasmfs file system (OPFS, IndexedDB), `FS.readFile( path )` appears to cause Safari browsers to freeze. Chrome and Firefox seem to work, but with a warning about blocking on the main thread. Perhaps there could be a way to access an OPFS file directly as a blob without using FS.readFile and not asynchronously?