Core: Introduce luautils::callGlobal helper

[zach2good]

I affirm:

• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
• I understand I should leave resolving conversations to the LandSandBoat team so that reviewers won't miss what was said.
• I have read and understood the Contributing Guide and the Code of Conduct.
• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Allow calling of functions in Lua from C++ without needing to manually prepare so many things for Lua, or to manually/dangerously access the lua state:

        luautils::callGlobal<void>("xi.server.onServerStart");

etc.

[zach2good]

Ready for review, works with hot-reloading. Will do some performance testing this week to see if we gain anything from the caching layer

[zach2good]

Trying to pin down why this is crashing during CS event updates inside LuaJIT

[zach2good]

This ended up shaking out a logical inconsistency that I can't understand why it wasn't crashing before.

When you extract something out of sol, it's lazy-evaluated. If you ask for lua[1][2][3] it won't evaluate until you do something with it. If you do lua[1][2][3]() it evaluates right away. We were pulling out a lua_nil from something, holding onto it for a bit, and then obj()[]ing into it without any additional checks.

I've added those checks in now.

It was around event string updates, so I've run it through the chocobo racing intro, which is the premiere spot for big event updates with arguments and strings.

I've logged in, I've done gobbie box, I've punched some lizards in the face, I've called out trusts and Sneak Attacked off of them, I've used items - everything seems stable now.

Ready to go 👍