Load current Memory start/size off of the wasm instance when entering
fast calls, so they can use that info for whatever they need to do.
Fast calls from JS set the memory to null, and the memory does not
need to be piped from wasm to slow callbacks as wasm always calls
the fast function.

Change-Id: Ibfa33cdd7dba85300f95cbdacc9a56b3f7181663
Bug: chromium:1052746
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3719005Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: snek <snek@chromium.org>
Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81538}