This was almost every case where we are overriding `respond_to?` in a
way that mirrors a parallel implementation of `method_missing`. There is
one remaining case in Active Model that should probably do the same
thing, but had a sufficiently strange implementation that I want to
investigate it separately.
Fixes#26333.
This has 2 effects:
1. RoutesProxy is CRAZY faster because it's no longer creating a new
Module each time method_missing is hit.
2. It bypasses an existing bug in ruby that makes `class << obj` unsafe
to be used in threading contexts.
