Add support for boolean operations betwen variants

[KoBeWi]

Fixes #44688

I had to split variant_op.cpp into multiple files, because of C1128 (file too big for debugging). The files need cleanup.
If you are wondering why the PR is so big, it's because it adds support for and/or between any Variant type, as it was in 3.x.

Also the code is broken. When I try to do any boolean operation in GDScript it fails, saying invalid operand. I don't know why ;_;

[KoBeWi]

Ok, so the problem is basically that the operators are stored in a static array. And for whatever reason, my function _register_variant_operators2(), which is defined in another file, uses a different array, despite it being the same static variable. After some googling it turns out that it's a common problem and static variables should only be defined in cpp files (apparently even header guards don't protect from multiple static definitions).

I have no idea where to put this array so that it properly compiles and works as expected. I give up. I hate C++ ;_;