Improve Native FileChooser File Filter Handling

From a pure UX perspective, it would be better to allow a dialog window to show the extension to save to, where you pick an extension as your target from the provided drop-down.

Ideally, this would be an array of FilterFilter (eg: OwnedArray<FileFilter>) to be selectable by a user so as to choose an extension to save a file to.

Preferably, this change would allow to differentiate the file type from the description (eg: .mp3 from MP3 (Lame)).

In our present case, what we get right now is extension pukeage: the user still has to break from the flow and manually type out the extension, which is unnecessary confusion.

What we get:

What I’d like: