Make top-k queries fast when static scoring signals are incorporated into the score

Block-max WAND (LUCENE-8135) and some earlier issues made Lucene faster at computing the top-k matches of boolean queries.

It is quite frequent that users want to improve ranking and end up scoring with a formula that could look like bm25_score + w * log(alpha + pagerank) (w and alpha being constants, and pagerank being a per-document field value). You could do this with doc values and FunctionScoreQuery but unfortunately this will remove the ability to optimize top-k queries since the scoring formula becomes opaque to Lucene.

I'd like to add a new field that allows to store such scoring signals as term frequencies, and new queries that could produce log(alpha + pagerank) as a score. Then implementing the above formula can be done by boosting this query with a boost equal to w and adding this boosted query as a SHOULD clause of a BooleanQuery. This would give Lucene the ability to compute top-k hits faster, especially but not only if the index is sorted by decreasing pagerank.