Instead of updating the detected features set directly, use the
synchronized {OnCompilationStopped} method.
In order to avoid this error in the future, the whole
{detected_features()} getter is removed, as it returns a pointer which
can only be accessed when holding the mutex anyway. Also, the refactored
code was the only user of this dangerous method.

Drive-by: Pass the WasmFeatures set by value, since it's just an
EnumSet.
Drive-by 2: Remove a print line from the regression test which can be
confusing if the test is picked up again by foozzie.

R=ahaas@chromium.org
CC=zhin@chromium.org

Bug: v8:11357
Change-Id: I75b5c8f35983d2bc1fd2b61adcb2ecfc18564f39
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_isolates_rel_ng
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2653226Reviewed-by: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72375}