Add jkummerow, thibaudm, zhin; drop titzer.
Also make src/wasm/OWNERS the source of truth and let test-specific
OWNERS files refer to that.

No-Try: true
Change-Id: I9862ae452970e20b7842269721ad6a7953f275fc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1989827
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65636}