Creates two different functions specialized for string and boolean
types.

Gets rid of several allocations and keeps the C++ <-> JS type
conversions to a minimum. Improves the API as we don't have to create
the fallback or V8 Strings unnecessarily.

Bug: v8:5751
Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: I788e43e6ef23f3e9144ff719f01d6334fe6cb9ce
Reviewed-on: https://chromium-review.googlesource.com/1126750
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54259}