Core: Protects against: 'from + size > scoreDocs.length' in case only single shard response
Core: reuse Lucene's TermsEnum for faster _uid/version lookup during

Reusing Lucene's TermsEnum for _uid/version lookups gives a small
indexing (updates) speedup and brings us a closer to not having
to spend RAM on bloom filters.

Closes #6212