This adds a flag to print a message on important GC events, like
triggering a GC, reporting live code per isolate, and finally deleting
dead code.
This helps debugging issues with wasm code gc.

R=mstarzinger@chromium.org

Bug: v8:8217
Change-Id: I901199bc19b2a8718728a9e4918c30e295e0e92a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1585842
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61075}