WBQC uses `WikiPageEntityMetaDataLookup` to get the latest revision IDs for a list of entity IDs, but that lookup actually gets a lot more information than we need, joining three large tables (`page`, `revision`, `text`) in the process. We don’t need that – for just the revision IDs, `page.page_latest` should be enough.
Part of https://wikitech.wikimedia.org/wiki/Incident_documentation/20180226-WikibaseQualityConstraints.
#patch-for-review:
- [x] [introduce method](https://gerrit.wikimedia.org/r/415258)
- [x] [minor refactoring](https://gerrit.wikimedia.org/r/415277)
- [x] [optimized implementation](https://gerrit.wikimedia.org/r/415278)
- [x] [documentation](https://gerrit.wikimedia.org/r/415831)
- [ ] [optimized implementation in PrefetchingWPEMDA](https://gerrit.wikimedia.org/r/415901)
- [x] [rearranged implementation](https://gerrit.wikimedia.org/r/416410)
- use new method
- [ ] [in WBQC](https://gerrit.wikimedia.org/r/415865)
- in Wikibase?