Attached is an improved patch, still not perfect but better.
I added Uwe's suggestion of delegating all methods in the wrapper, and also
setting the rewrite method in the ctor and documenting that it does this.
I added a simple test case in search.spans that wraps some wildcard and fuzzy queries,
and added examples and javadocs.
I also deprecated the SpanRegexQuery, converted the tests for the contrib SpanRegexQuery to use the wrapper directly, and deprecated the old tests, but they still work too.
I would prefer to avoid the heavy refactoring of MultiTermQuery rewrites (easier on another issue?) just because it would make backporting to 3.x a little more tricky.
Anyway, I think this is pretty close, maybe just needs another police investigation