st/oxr: Centralize the lists of subaction paths using x-macros.

Goal here was to avoid the incomplete and haphazard duplication of the lists of subactions paths that were scattered around. Hopefully we can just use these x-macros from the centralized oxr_subaction.h header to do 90% of the things we need that involve iterating through the subaction paths, and thus would only have two lines (in one file) to modify when the set of subaction paths changes.

Inspired by seeing more of these sequence-of-ifs land in a recent MR.