This new method returns no value and just verifies that the Maybe is not
Empty. This is intended to be used for functions like Object::Set that
return a Maybe<bool> but only use "emptiness" to indicate its result and
where ToLocalChecked() appears to be discarding information.

Also comments Object::Set to indicate that Check() is the preferred way
of asserting that the Set should always succeed.

R=yangguo

Bug: v8:8562
Change-Id: Ic3b45e42fa9ba0b53f1a764660a56041e64f087b
Reviewed-on: https://chromium-review.googlesource.com/c/1414912Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58852}