chore: rename one of the builder.inc.sh includes

We need to rename resources/builder.inc.sh so we don't get confusion between it and resources/build/builder.inc.sh.

> No, we have two `builder.inc.sh` scripts. `resources/build/builder.inc.sh` behaves as you describe (and outputs a warning if you don't call `builder_describe`), but `resources/builder.inc.sh` is meant to be used outside of builder scripts.

Oh that's right. My bad. I think we should rename one of them ... it's very confusing. I will consider doing that in 19.0 maint.

_Originally posted by @mcdurdin in https://github.com/keymanapp/keyman/issues/13754#issuecomment-2837508384_