The hextobin tool is used to help us construct invalid .kmx files
without having to either hack these into the compiler, or write them
with a hex editor. It feels a little bit of overkill, but this makes it
easy to (a) work with our intended file structures, and (b) review any
changes to these invalid keyboard tests.

Note: I did do a cursory search for a hex2bin or hextobin that we could
easily use but did not find a good simple cross-platform tool that we
could consume (`xxd -r` would work but AFAICT constrains our format to a
dump which is much harder to work with and read -- I wanted to be able
to annotate with file structures.)

For an example, see ik_000_null_invalid.txt.

This means that building the invalid keyboards for tests requires node,
but that should be fine given we need node to build the valid keyboards
anyway.

I've put hextobin under core/tools but it could just as well live under
common/tools in the future, if we find it useful for other project unit
tests.

Removes .kmx from repo and builds them from the source .xml files using
kmldmlc (building that if necessary also with a poor fella's dependency
check for now), and generally a lot of cleanup of the meson.build files
for the ldml tests.

Moves keyboards to a subfolder of the ldml unit test folder to keep them
neat and tidy and avoid embedding huge files into ldml.js for test of
WASM.

Note: 000_null_keyboard and 002_null_invalid do build successfully, but
the core ldml keyboardprocessor currently fails on them, because they
are missing keys and vkey sections.

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 🙀