Adds VERB_REF and derivative (#74500)

Apparently in (one) place in the codebase, we were still using stuff
like `.verb/example_verb` for stuff like `INVOKE_ASYNC()` and
`CALLBACK()`s, and I'm pretty sure this is one of those things that are
being phased out in 515 (like we had to deal with in
4d6a8bc5371eb61f9adb7c4dd1b8c441d3ae9251), so let's give it the same
treatment as we did `PROC_REF` in November 2022.

In order to make this work, I created a generic backend of define
macros, and then moved two things: `PROC_REF` and `VERB_REF` to just
leverage that backend as needed. This was done just so we didn't have to
copy-paste code in case we needed to update these macros in the future,
let me know if I should approach this a different way.

code don't break (or at least the compile-time assertions won't break)
when we inevitably fully shift to 515. whoopie!

Nothing players should be concerned about.