**Context**
`TermSqlIndex` is still the only implementation of `LabelConflictFinder` that is used to find conflicts in labels and descriptions when creating properties and items, that is used in few places such as `LabelUniquenessValidator`.
**Problem**
We will not be able to stop writing to both term stores before we provide an implementation that looks up possible conflicts in the new store.
**Solution**
Provide a new means (interfaces + implementations) that allows writing uniqueness validators using the new store
Check if there are indexes on new tables to support this.
**Todo**
[] add implementation for detecting label and label+descripton collisions [[ https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/546898 | patch for review ]]
[] add validator implementations using the above two collision detectors
[] wire up the new validator when reading from new store (migration values of `MIGRATE_WRITE_NEW` or `MIGRATION_NEW`)