Uses the JavaScript BigInt Object to represent Wasm's 64bits integers.
Attention, 32 bits architectures are not supported yet.

Bug: v8:7741
Change-Id: I28b718fa567bca5103b2f38a879049cd20a46f12
Reviewed-on: https://chromium-review.googlesource.com/c/1355144
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58152}