Implements basic LDML keyboard xml loader and compiler.

Merge pull request #7113 from keymanapp/revert-7112-revert-7110-feat/developer/ldml-constants-ts-module

feat(core): turn @keymanapp/ldml-keyboard-constants into a module 🙀

feat(developer): LDML compiler kmx-builder 🙀

feat(developer): groundwork - kmx file structures 🙀

Co-authored-by: Marc Durdin <marc@durdin.net>

Co-authored-by: Marc Durdin <marc@durdin.net>

- vkey and loca needed padding before the variable part
- add static asserts to validate this padding
- update sample files (null and tiny)

#7043

- also update test case, 002_null_invalid is expected to not validate

#7097

chore(core): update 000_null_keyboard to be a proper null keyboard 🙀

- also update test case

#7097

Merge branch 'revert-7112-revert-7110-feat/developer/ldml-constants-ts-module' into feat/developer/ldml-compiler-kmxplus-builder

Adds support for writing kmxplus section of a kmx file. Extends KMXFile
to a KMXPlusFile subclass. Adds KMXPlusBuilder which is called from
KMXBuilder if KMXBuilder finds that the file is a KMXPlusFile.

This means that KMXPlusBuilder generates a buffer that could be stored
independently of its parent .kmx file transport, if that is later
considered desirable.

Adds new constants for sizes of various table components, which makes
building the file much simpler.

chore(developer): Merge branch 'feat/developer/ldml-compiler-kmx-structures' into feat/developer/ldml-compiler-kmx-builder

- rewrite 000_null_keyboard.kmx to be valid, but with no keys
- remove outdated comment in kmx_plus.h
- update kmx_plus.cpp to not reverse the order of section ids (#7098)
- add a new test option for expected-error

fix(core): fixes for kmx_file rearrangement 🙀

fix breaks in #7111 and prior

- try stdint.h instead of cstdint

#7098

fix breaks in #7111 and prior

#7098

Revert "feat(core): turn @keymanapp/ldml-keyboard-constants into a module 🙀"

chore: merge master into feature-ldml

feat(core): turn @keymanapp/ldml-keyboard-constants into a module 🙀

fix(core): ldml: remove 0-length arrays 🙀

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.

feat(common): add parameter variable support to `builder_` functions

Generates a valid .kmx file (legacy structures only) from an
intermediate in-memory structure. Included for completeness, although it
is anticipated that LDML keyboards will not have any groups, though they
will probably have some metadata stores.

#7098