feat(common): embed .kvk, .keyman-touch-layout in .kmx

For web core, it would be ideal to embed .kvk and .keyman-touch-layout data into the .kmx. This would enable us to distribute a single .kmx file for web. Long term, we can deprecate having separate .kvk files also. For 18.0, only web core would use the metadata.

Questions:
* Binary format or embed json? (preferably binary, definitely do not embed XML)
* Unify touch layout and kvk? (yes)
* Can we just use the KMX+ tables? (yes)

Projects:
* add flag to .kmx to identify that file includes KMX+ OSK data
* design any other file format changes + document in schemas
* build conversion tool from kvks+keyman-touch-layout into a single ldml keyboard source, and pass that to ldml compiler to generate ldml tables

Notes:
* do not embed font data from these formats -- apps should use font data from kmp.json or other sideband metadata.
* consumption of these tables for desktop platforms is v20

See also:
* #12695