Move into its own new function the the low-level logic to search for a given RNA path in Action F-curves, then driver F-curves of a given AnimData. This deduplicates code from `BKE_fcurve_find_by_rna_context_ui` and `id_data_find_fcurve`, and will allow for future more usages of this functionality. Differential Revision: https://developer.blender.org/D15068