[tlbuild] LuaMetaTeX for TeX Live

[Mojca Miklavec]

Dear Karl,

Today Hans has announced the new version of LuaMetaTeX which will
officially live under
    https://github.com/contextgarden/context/tree/main/source/luametatex
and will be distributed together with ConTeXt sources.

It would be really awesome if the luametatex binaries could end up in
TeX Live 2023.

The build is done using CMake, so I'm not sure about the best way to
integrate it into the current autotools-based toolchain.

We've been building it on our farm for a while (it generally takes
less than 1 minute for a complete build):
    https://dl.contextgarden.net/build/luametatex
    https://build.contextgarden.net/#/waterfall?tags=c.luametatex
so the binaries for most relevant platforms are already available (and
could be made available at particular commits/branches to match what
goes into TL 2023 for example), but I'm not sure if that counts as
acceptable. We are missing binaries for netbsd, cygwin and signed
macos.

Mojca