Big quantum_keycodes cleanup

[fauxpark]

Description

Hoo boy.

• Moved Swap Hands range to 0x5600, just to fill in that gap
• Pulled range aliases (MIDI velocity min/max etc.) out of the enum and into defines at the end of the file
• Annotated every keycode with its value in hex, up to the Sequencer keycodes - they still have yet to be made static, but at least they're at the end, for now
• Removed all the ifdefs! And via_ensure_keycode.h doesn't complain! This does mean that everything guarded by an ifdef had to be moved to the end of the enum, though
• Tweaked/added/improved some comments

As mentioned, this doesn't break VIA, but it does shuffle some values around, so perhaps this should go into develop instead?

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[drashna]

Also, I think the keycodes from via should be moved out of via.h, and into quantum_keycodes.h, at some point.

[tzarc]

Should this stay on master or go to develop?

[fauxpark]

Should this stay on master or go to develop?

I'm not really sure. On one hand, VIA remains unaffected by this, no keycode values it knows about are changed, and the ones that are it doesn't know about yet.
On the other hand, this is a large enough change, breaking or no, that it could possibly be considered develop-worthy...

Personally I would rather get this into master, as that allows VIA to start work on adding support for more keycodes faster.

[drashna]

thanks!