[CHORE/FEEDBACK WANTED] Cleanup polymod.hscript._internal - #522

As things are inevitably added and improved on within the scripting system for Polymod, things are bound to get messy for the codebase of some files (and debatably already have).
This PR doesn't necessarily add really anything new but instead tries to make all internal hscript-related files as clean as possible by:

• Staying consistent with the established codestyle of other files within the library.
• Re-ordering functions and fields are appropiate to help with readability.
• Adding documentation so it's easier for people to understand what their purpose is.

This isn't done yet! Which is why this is a draft as well to get feedback from other contributors and maintainers if possible on their opinions on this before putting it for full review.

Small things this PR also has:

• Makes sure PolymodScriptClass is ALWAYS instantiated using PolymodStaticClassReference.instantiate (this is a MUST because of how superclasses work now)
• Makes sure using functions cache of script enums are cleared when scripts are reloaded.