The fast path for IsExtensible proxy trap is already implemented, we just need to use this for ReflectIsExtensible.
Now, ReflectIsExtensible is now a Torque builtin (previously CPP). Other cases will fall back to runtime.

Bug: v8:6664
Change-Id: Ib1c3f78d1f1a44c6628d351fed3bcdc91ca08cb5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1645438Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Tamer Tas <tmrts@chromium.org>
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#62031}