Specify some ogg encoder options

[RblSb]

I'm not sure if {ffmpeg_ogg_options} is preferred way to specify this, instead of just adding these args in main directly. I refactored options extraction part a bit into a more functional style, i hope it looks a bit better.

And maybe we also need to specify output sampling rate? I just don't get if stb vorbis wants 44100, 48000, or it doesn't matter and can be custom.

• Also updated to es2019 to access array.flat method

[RobDangerous]

Sampling rate shouldn't matter. Ideally input == output but the output sampling rate is different on different systems.
Can't we just always set those ogg options for ffmpeg?

[RblSb]

If you think parts.map() refactoring is not better than double for, i can reopen this PR as one line options.ogg args change instead. I just got confused by for (arg in args) and decided to rewrite that block.