Core: Introduce luautils::callGlobal helper and more caching (big performance improvement ⏩)

[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