Towards standard usage of ExtendedRewriter (#7145)

Towards standard usage of ExtendedRewriter (#7145)

This PR:

Adds extendedRewrite to EnvObj and Rewriter.
Eliminates static calls to Rewriter::rewrite from within the extended rewriter. Instead, the use of extended rewriter is always through Rewriter, which passes itself to the ExtendedRewriter.
Make most uses of extended rewriter non-static. I've added a placeholder method Rewriter::callExtendedRewrite for places in the code that call the extended rewriter are currently difficult to eliminate.