Aggregations: Do not take deleted documents into account in aggregations filters.

Since aggregators are only called on documents that match the query, it never
gets called on deleted documents, so by specifying `null` as live docs, we very
likely remove a BitsFilteredDocIdSet layer.

Close #8540
Aggregations: Fix geohash grid aggregation on multi-valued fields.

This aggregation creates an anonymous fielddata instance that takes geo points
and turns them into a geo hash encoded as a long. A bug was introduced in 1.4
because of a fielddata refactoring: the fielddata instance tries to populate
an array with values without first making sure that it is large enough.

Close #8507