Move EnumString to separate file and add enum_to_string

[cx384]

This PR only moves code and adds enum_to_string, so it should be easy to review.
(As mentioned in one of my other PRs #15681)

c_types.h now only contains LuaError and StackUnroller, and includes improved.

(At first, I implemented a very fancy templated enum <-> string conversion handler to do as much as possible at compile time, but the improvement was questionable not really worth the change, so I kept our EnumString.)

Note:
Only es_HudBuiltinElement does not use enum_to_string, since it behaves a little different.

es_ItemType and es_TouchInteractionMode are (currently) only needed in c_content.cpp so I moved them there, IMO it's better than keeping them in c_types.h.

To do

Ready for Review.

How to test

I don't know.

[sfan5]

lgtm