Update app route handler proxy handling (#47088)
This ensures our Proxy wrapping request fields works properly in the
edge-runtime by explicitly binding to the correct request instance.
x-ref: [slack
thread](https://vercel.slack.com/archives/C03UR7US95F/p1678730563467089?thread_ts=1678662292.695769&cid=C03UR7US95F)
