Extract commonly used instantiate() and evalWithUrl() functions.

Bug: chromium:1093165
Change-Id: I14f8b49d556bc70d2092a80b41c5bbf678efd1a9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2245599
Commit-Queue: Kim-Anh Tran <kimanh@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68356}