This seals any surrounding {HandleScope} when the interpreter enters the
main interpreter loop. It ensures that there are no accidental leaks of
handles into the surrounding scope and enforces that operations dealing
with handles open their own scope.

R=clemensh@chromium.org

Change-Id: I43d479129bef60beb7565022b24577f8bf1dc522
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1550401Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60601}