If an output operand has "same as input" policy, we cannot assume that
it's input 0. Instead we should look at the {input_index}.

The bug manifests on Wasm select instructions, where the input index is
actually 2 and not 0.

In order to test this better, we introduce the a new
--turbo-force-mid-tier-regalloc flag, which always uses the mid-tier
register allocator. Otherwise the bug would only manifest on huge
functions.

R=mslekova@chromium.org
CC=​thibaudm@chromium.org

Bug: v8:12330
Change-Id: I6a005a48bbd2aba354dc99fed587bffce24c8839
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3234722Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77495}