Make all track menu commands available for scripting / macros

### Your idea

Most of the track drop-down menu commands are available for scripting / macros, with some notable exceptions:
* Make Stereo Track
* Swap Stereo Channels
* Split Stereo Track
* Split Stereo to Mono
This proposal is to make these missing commands available for scripting / macros.

### Problem to be solved

Via scripting / macros:
* It is not possible to combine mono tracks to stereo without processing the tracks (much slower than "joining" the tracks).
* It is not possible to swap stereo channels without processing the track.
* It is not possible to split stereo tracks without duplicating and mixing down.
All of these operations are much more complicated and much slower than they need to be.

### Prior art

_No response_

### Additional context

This feature has been asked about on several occasions, including a recent question on Audacity Discord.