This fixes the debug code which checks that API callbacks
return only valid JS values: BigInt was missing from the list
of allowable types.

Bug: chromium:985115
Change-Id: I8b3db409bd99e9e9b936d520d0fdbe75654e7602
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1706623Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62812}