Also splits the root tsconfig.json into tsconfig.cjs.json and
tsconfig.esm.json. These are not typically used at present but in theory
you could do a `tsc -b <tsconfig.x.json>` and build all modules. In
practice, we still have some prebuild steps that make that a bit of a
pain.
Splits the building of keyboardprocessor_ldml.h into a separate
tsconfig.build.json, and designates keyboardprocessor_ldml.ts as a new
Typescript/Node module @keymanapp/ldml-keyboard-constants.
Includes an example usage in the (currently unused) kmx-plus.ts.
