Add LuaJ bindings

[gudzpoz]

This PR adds LuaJ bindings to LuaJava, hopefully serving as a placeholder for platforms without binaries (or not yet supported by jnigen). For example, iOS users may use LuaJ bindings since they are pure Java.

There are several caveats though:

1. A fork of LuaJ is used since the original one is unmaintained. However, the fork has yet to publish a Maven artifact, and before that, we need to use JitPack.

2. LuaJ uses Java threads (heavyweight before Loom) for Lua coroutines (generally lightweight). It can become a problem if the user uses coroutines heavily.

3. LuaJ does not provide Lua C API, upon which this library builds. A compatible layer is added, but there are several hidden behavioral changes in stack operations:

   When a LuaJ function is called, the library does not supply a lua_State-like pointer, which means we cannot possibly manipulate the stack from within the function. This is handled by tracking the thread that created the function / any value, while standard Lua operates on the current thread.

4. Thanks JNI, we were able to call the default function defined by interfaces. However, in LuaJ, this is not possible any more: all we have access to is Java reflection API.

5. LuaJ uses some classes that are introduced in Java 8 API but not available in lower Android API levels. We just don't test on those Android versions. (Having trouble setting up Android desugaring.)

These should have been documented in docs/?

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 94.36%. Comparing base (c5ff946) to head (3982e58).

Files	Patch %	Lines
.../iroiro/luajava/jsr223/LuaScriptEngineFactory.java	0.00%	0 Missing and 1 partial ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##               main     #164      +/-   ##
============================================
- Coverage     94.43%   94.36%   -0.07%     
  Complexity      610      610              
============================================
  Files            31       31              
  Lines          1455     1456       +1     
  Branches        184      184              
============================================
  Hits           1374     1374              
  Misses           64       64              
- Partials         17       18       +1     

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