Get output as File object from ffmpeg.FS

**Is your feature request related to a problem? Please describe.**
I want to input this into a JS library/plugin that only accepts File objects. Is there a way to do this? Currently I figured I can do it through this inefficient way:

```
const data = ffmpeg.FS('readFile', 'output.mp4');
var files = [new File(data, "output2.mp4")];
```

**Describe the solution you'd like**
Essentially get a File object directly.

**Describe alternatives you've considered**
Already mentioned above:
```
const data = ffmpeg.FS('readFile', 'output.mp4');
var files = [new File(data, "output2.mp4")];
```

**Additional context**
No