BooleanFilter and ChainedFilter miss to fully optimize for OpenBitSets [LUCENE-2724]

In line 65 of the BooleanFilter class there is an optimization for OpenBitSets, but i miss an optimization in line 62.

I would replace the existing line:

```Java
res = new OpenBitSetDISI(getDISI(shouldFilters, i, reader), reader.maxDoc());
```

with following code:

```Java
DocIdSet docIdSet = shouldFilters.get(i).getDocIdSet(reader);
if(docIdSet instanceof OpenBitSet) {
res = new OpenBitSetDISI(reader.maxDoc());
res.or((OpenBitSet) docIdSet);
} else {
res = new OpenBitSetDISI(docIdSet.iterator(), reader.maxDoc());
}
```

Same for line 78 and 95, adjusted for not and must filters.

That leads to an up to 5 times slower AND-combination in my test, where i had two filters to be AND-combined returning each a cached OpenBitSet, one with a cardinality of 15000 and the other with a cardinality of 13000. The result had a cardinality of 8300. Thats important if you do that 1000 times with a lot more documents.

The same must be also done for ChainedFilter in the method initialResult(..).

Also, the getDISI method in the BooleanFilter must be replaced by a getDocIdSet(..) method. This is useful because in line 87 the docIdSet is retrieved and in line 92 again when it is not of type OpenBitSet. This may also lead to a performance issue if the getDocIdSet method of a sub filter is not super fast.

---
Migrated from [LUCENE-2724](https://issues.apache.org/jira/browse/LUCENE-2724) by Fatih Uzdilli

Read BooleanFilter around lines 62, 65, 78, 87, 92, and 95, then inspect ChainedFilter.initialResult(..). Verify the OpenBitSet optimization and single DocIdSet retrieval across the should, not, and must filter paths, with the reported AND-combination performance improvement as the completion criterion.

Written by the indexing model from the issue text.