Update Swiss French/German keymaps and add sendstring LUTs

[fauxpark]

Description

🇨🇭 (🇫🇷/🇩🇪)

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.
• 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).

[vomindoraan]

It would be nice to see {keymap,sendstring}_fr_ch.h renamed to {keymap,sendstring}_french_ch.h for consistency. It's only used in a couple of community layouts as far as I can tell, so renaming it shouldn't be too bad.

[vomindoraan]

Consider using CH_* instead of FR_* and DE_*, since the Swiss layouts are more closely related to each other than they are to the regular French and German layouts. Also, CH_* would be in line with the current practice of using country codes as prefixes, whereas FR_* and DE_* would not.

[fauxpark]

I would probably want to rename the whole lot to match fr_ch, but that would be quite the breaking change. For the moment, I could rename these to {keymap,sendstring}_{french,german}_swiss.h and have the original headers simply include the correct ones, perhaps with a #pragma message indicating they are deprecated.

[vomindoraan]

That sounds good to me.

In my opinion, the best solution in the long term would be to name the files by locale (as discussed in #8560) and the keycodes by country code (for brevity). So Swiss French would use keymap_fr_ch.h, as you suggested, with CH_* keycodes; Serbian Latin would use keymap_sr_latn.h with RS_* keycodes; Brazilian Portuguese would use keymap_pt_br.h with BR_* keycodes; etc.
We could implement this in the upcoming breaking change, and I'd be glad to assist you.

For the time being, though, {keymap,sendstring}_{french,german}_swiss.h is the way to go.

[vomindoraan]

LGTM, just rename the files when you get the chance.