Add an event for recording metrics related to decoding Wasm modules.

R=clemensb@chromium.org

Bug: chromium:1092417
Change-Id: Id60560d8eb8c14edb5b863857b18c1c82f48e7e7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2351672
Commit-Queue: Emanuel Ziegler <ecmziegler@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69425}