Internal private struct was using `owner_id`/`self_id`, while the public callback data struct was using `id_owner`/`id_self`. Now using internal naming everywhere in lib_query related code, as `owner_id` is already used in very low-level 'fundamental' part of the code, e.g. in the `PointerRNA` struct, or in ID's 'loopback' pointers for embedded data. Note that this is only a very small first step toward proper naming consistency for these type of data, the mismatch is currently spread all over the code base. We also need to document more formally the meaning and differences between `self` and `owner` here.