Add support fo LuaU

[gudzpoz]

Discussed in https://github.com/gudzpoz/luajava/discussions/178

^{Originally posted by **osp54** June 2, 2024} Сan you add support for [LuaU](https://github.com/luau-lang/luau)? It has compatibility with lua51(in embedding too), and is its typed superset.

[gudzpoz]

LuaU is not fully compatible with Lua 5.1 C API. And to add to it, the incompatibilities are not well documented yet, making it extra hard to support or to catch up with any breaking changes that might follow.

Currently I don't think I have enough motivation (or energy) to support it (since it can potentially break too many things), but I will happily review any PR that aim to bring such support.

I will summarize the challenges here for anybody that is willing to work on this:

• __gc is not supported in LuaU, while LuaJava uses it to cooperate with Java GC. The code using __gc is under jni/luajava/jua.cpp and you will need to rewrite it for LuaU by presumably using lua_newuserdatadtor along with a bunch of #if macros.
• The Lua C bindings in LuaNatives are generated with scripts under scripts/ that scrape lua.org manuals. Since LuaU does not offer a manual page, you will probably need to write a script to parse the C header files instead.
• LuaU may not provide all C API in the LuaNatives interface. If not, you will need to implement those functions yourself, similar to https://github.com/gudzpoz/luajava/blob/e0c39fd5b7c5a5b5425dcb2ef51bfd7910fe438a/lua51/jni/mod/luacomp.h#L17-L20
• LuaU uses C++ and CMake. (By comparison, Lua 5.N uses plain C and allows amalgamation builds.) And you will need a rather complex building script like luajit/build.gradle to first get a static libluau.a library and then link jnigen code against it. I consider this step most challenging (and a bit tiresome) as we need to support all those platforms...