feat(common): LDML keyboards need to support font association for OSK

[mcdurdin]

I had started this as an LDML keyboard (which doesn't support mobile), but when I realized I couldn't associate a font with it, and the OSK was square boxes, I switched to a regular .kmn structure instead of LDML.

Originally posted by @LornaSIL in https://github.com/keymanapp/keyboards/issues/3170#issuecomment-2452467508

[LornaSIL]

• The only way to test the OSK seems to be to install the keyboard.

• When I install the keyboard, the OSK is too small to take a screenshot for documentation purposes.

• There is no way to export the layout for documentation purposes.

• The cute little icons are fun, but we can't do those. Not a show stopper!

• I had wanted to set the script for RTL for the Imperial Aramaic keyboard and didn't see where to do it. However, it seemed to figure it out on it's own based on the script in use apparently.

Those are the main drawbacks I ran in to for both dives_akuru_inscript and Imperial Aramaic. There is likely documentation that I couldn't find, but I had to use several sources to figure out the syntax for how to access RALT and RALT+shift keys.

I can attach my sources for both keyboards if that would be useful.

[mcdurdin]

Thanks @LornaSIL -- we don't need the source at present. These comments are helpful as we try to get LDML keyboard editing and documentation done in the next year.