Major Description
Today it's limited to 32, because it uses a separate bit in the mask
for each clause.
But I don't understand why it does this; I think all prohibited
clauses can share a single boolean/bit? Any match on a prohibited
clause sets this bit and the doc is not collected; we don't need each
prohibited clause to have a dedicated bit?
We also use the mask for required clauses, but this code is now
commented out (we always use BS2 if there are any required clauses);
if we re-enable this code (and I think we should, at least in certain
cases: I suspect it'd be faster than BS2 in many cases), I think we
can cutover to an int count instead of bit masks, and then have no
limit on the required clauses sent to BooleanScorer also.
Separately I cleaned a few things up about BooleanScorer: all of the
embedded scorer methods (nextDoc, docID, advance, score) now throw
UOE; pre-allocate the buckets instead of doing it lazily
per-sub-collect.