This turns some CHECKs in the mid-tier register allocator into DCHECKs.
The ones inside {CheckConsistency} should be DCHECKs anyway, even if
they are inside an "#ifdef DEBUG" block. This will make ClusterFuzz
correctly detect them as "checks that only happen in debug mode".
Others were just unnecessarily always included, instead of only in debug
builds.

R=thibaudm@chromium.org

Bug: chromium:1271369
Change-Id: I51acde3c951c7a2af9dee36e25b196364ddf8f5c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3406760Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78741}