This introduces `LeafCollector#collect(DocIdStream)` to enable collectors to
collect batches of doc IDs at once. `BooleanScorer` takes advantage of this by
creating a `DocIdStream` whose `count()` method counts the number of bits that
are set in the bit set of matches in the current window, instead of naively
iterating over all matches.

On wikimedium10m, this yields a ~20% speedup when counting hits for the `title
OR 12` query (2.9M hits).

Relates apache#12358