The new API supersedes the old `RegisterDefaultSignalHandler` and flag
combination. Now the embedder must explicitly call
`EnableWebAssemblyTrapHandler` to activate the trap handler and optionally
install the default signal handler. The old flag is now used only by D8 to
decide whether to call this function.

Bug: v8:5277

Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I05fbb2138138bfc95b14361aabd712db84789b4a
Reviewed-on: https://chromium-review.googlesource.com/963179
Commit-Queue: Eric Holk <eholk@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52081}