Conditions are usually used in binary comparisons, and are named for
that purpose. When used in a unary comparison, {kEqual} means "equal to
zero" and {kUnequal} means "not equal to zero". This is noted in several
comments in {LiftoffCompiler}.

This CL introduces the alternative names {kEqualZero} and
{kNotEqualZero} to avoid the repeated comments and increase readability.

R=thibaudm@chromium.org

Bug: v8:12244
Change-Id: I720a3d91ea95a26a38a48c68161f1b0552937cd4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3172763Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76964}