After allocating a new code space, we do some initial allocations in the
new space (e.g. for the jump table). These allocations are not allowed
to fail.
If this in indeed what's happening in the linked bug, this CHECK will
give fuzzers a chance to find us a reproducer.

Drive-by: Introduce {WasmCodeAllocator::kUnrestrictedRegion} to remove
magic constants.

R=ahaas@chromium.org

Bug: v8:1111266
Change-Id: Ia76721653226bd4aa346b89ffab0c80f67892794
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2333250
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69204}