Port d303f4fb

Original Commit Message:

    In the past we've used the isolate argument to signal whether we were
    in unicode mode (nullptr) or not (the real isolate). This is no longer
    needed, and in fact breaks no-i18n mode which always expects to have a
    real isolate.

R=jgruber@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: I2b8ede3c89738a6cec59f8e32657a3c8c815fe6a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2081888Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#66534}