Call it NativeContextRef::GlobalIsDetached and implement it on top of
Refs such that it can benefit from direct reads.

Drive-by: inline a JSNativeContextSpecialization::ReduceGlobalAccess
overload into its only callsite.

Bug: v8:7790
Change-Id: I1c6891e0fc65a476b0c4587f3fde2c6461b302a4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2959614Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75454}