Instead of looking up the register holding the instance parameter, and
checking that this is the constant we expected, do it the other way
around: Use the constant, and check that this matches the information in
the CallDescriptor. This saves a few instructions on every Liftoff
function compilation.

Drive-by: Move comments, checks, and code emission closer together.

R=thibaudm@chromium.org

Bug: v8:11384
Change-Id: If51425479ded4f271de231479c21e24acefe7f35
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2692575Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72735}