Use the type specified for StoreField and StoreElement to check whether
we are storing a TaggedSigned value, and skip the write barrier for the
write completely in that case.  Also make sure to set that field type
appropriately for JSGlobalObjectSpecialization.

R=jarin@chromium.org
BUG=v8:4470
LOG=n

Review URL: https://codereview.chromium.org/1410743009

Cr-Commit-Position: refs/heads/master@{#31772}