Hadrian: install patches 'haddock-{html,interface}'

Since the $(docdir) can be picked independently from the $(libdir), we need to make sure that that the haddock-html and haddock-interface fields in the package DB (which is in the $(libdir)) get updated to point to the appropriate places in the $(docdir).

NB: in the make system, ghc-cabal would cover this sort of thing by re-running configure on installation, but here we get away with a couple lines of sed and a call to ghc-pkg recache.

Fixes #16202 (closed).