Enables WebAssembly's js-api module/customSection. The specification has
been updated; see https://github.com/WebAssembly/spec/issues/915. V8 was
already using DOMString.

Bug: v8:8633
Change-Id: I4c3e93c21594dbba84b3697e7e85069c3ff8b441
Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Reviewed-on: https://chromium-review.googlesource.com/c/1415554
Commit-Queue: Sven Sauleau <ssauleau@igalia.com>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59182}