Aggregations: apply 'from' if there is one shard result.
Core: apply 'from' if there is one shard result.
[TEST] speed up HighlightSearchTests a bit

Randomize rewrite methods instead of trying them all when highlighting multi term queries with postings highlighter
Rely on search type randomization and remove all the explicit setSearchType calls as they are not needed anymore
Remove explicit `.from`, `.size` and `.explain`, not needed and might slow tests down (especially explain)
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
Add ability to restore partial snapshots

Closes #5742