ObjectIsExtensible is now a Torque builtin (previously CPP) and the Proxy path is implemented completely in Torque while everything else calls into runtime (and is thus a bit slower than previously).

Improvement in micro-benchmark
Before:
IsExtensibleWithoutTrap-Proxies(Score): 2228
IsExtensibleWithTrap-Proxies(Score): 917

After:
IsExtensibleWithoutTrap-Proxies(Score): 3683
IsExtensibleWithTrap-Proxies(Score): 3310

Bug: v8:6664
Change-Id: I1fbe1c51cb724a23d7a59fc8231bb3d1461a6add
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1637444
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62006}