Live ranges defined by a constant operand normally don't require a spill
slot since they can just rematerialize the value from the constant. In
the attached issue however, deoptimization adds an explicit slot
requirement for a range that is defined by a constant operand. This case
is not expected in the register allocator and we eventually hit a
DCHECK.

This fix allocates a new stack slot during the MeetRegisterConstraints
and adds the missing gap move.

Drive-by: remove dead method LiveRange::NextSlotPosition.

R=sigurds@chromium.org
CC=​nicohartmann@chromium.org

Bug: chromium:1146880
Change-Id: I08fbb890f2f3d9574196989cf3e5ef6232433484
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2563689Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73510}