Make GetValueType to generate only function signatures
to avoid default values in new_object.

Bug: v8:11954
Change-Id: Ia6ebdde0a9c10c56afef29d6db3b3266816210e3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3158222Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Rakhim Khismet <khismet@google.com>
Cr-Commit-Position: refs/heads/main@{#76934}