Enable flexible Query.rewrite [LUCENE-8184]

I think `Query.rewrite(IndexReader)` should be generalized a bit to enable users to customize the rewrite process outside of the Query classes (i.e. without having to create a custom Query just to implement rewrite).  This could be as simple as having rewrite accept a QueryRewriter parameter that has a method that accepts a Query to be rewritten.  Only this method would call rewrite on any given Query.  And given very few spots actually use the IndexReader arg, we could even remove that as a parameter and add a getter to QueryRewriter (which is allowed to return null).  Or create a subclass e.g. QueryRewriterWithIndexReader if some prefer casting; debatable.
 
Today, users have to hard-code Lucene class names with related logic for each one.  This is obviously annoying/tedious, and brittle as Lucene adds to queries, and tends to be duplicative.  Examples of why an app might want to rewrite a query:
- to replace position-sensitive queries that are not already SpanQuery's with their SpanQuery equivalent.  This is useful in highlighting – Luwak's SpanRewriter does this.
- to simplify BooleanQuery's to a canonical form, or other canonicalization such as BoostQuery boost of 1.  The point is to simplify or strengthen the accuracy of query examination logic for whatever further purpose (e.g. routing a query for an optimization).  
- to replace one field for another
- to "fix" pure negative queries so that they work (by adding a MatchAllDocs query).  I'm surprised we still live with this.
- to relax a query that doesn't match to a looser one that does (e.g. manipulate minimumNumberShouldMatch) without re-parsing the query.  Granted re-parsing affords using different analysis or other strategies.
- to make it easier to use a Lucene Query class as a base class during query parsing/building. You could rewrite to strip out/replace only the AST nodes and leave the real Lucene Queries as-is.

Finally until #4114 is addressed (generic Query visitor) a customizable rewrite would allow a generic query visitor using a QueryRewriter that doesn't actually rewrite anything.  It's a little abusive as it's doing wasted work and no rewrite is actually occurring, but I think the overhead needn't be that much and such a use-case might even special-case BooleanQuery in particular to lower the overhead further. Basically for known many-child aggregator Query classes, customize to simply delegate.

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Migrated from [LUCENE-8184](https://issues.apache.org/jira/browse/LUCENE-8184) by David Smiley (@dsmiley)
Linked issues:
- #4114

Start with Query.rewrite(IndexReader) and the linked #4114 discussion. Compare the proposed QueryRewriter designs and their IndexReader behavior; done means callers can customize query rewriting without creating custom Query subclasses, with the chosen API and compatibility behavior covered by tests.

Written by the indexing model from the issue text.