fix(developer): kmc-package support for keyboard metadata

Fixes #9208.
Fixes #9209.
Fixes #9203.
Fixes #9198.

The changes here overlap in kmp-compiler.ts. Addresses several issues
with the package compiler:

* refactors the reading of the metadata from keyboards to make use of it
  when refreshing the keyboard metadata in kmp.json (#9208). This is the
  bulk of the changes.
* Fixes case on some fields in the kps file format (#9209)
* Removes code which emitted strings table to kmp.json, as these were
  only ever used for package installer executables (#9203)
* Cleans up code which emitted Start Menu items to make it match spec
  (#9198)