The SourceRangeScope helper was consuming too many characters, instead
explicitly create SourceRange, based on scanner position.

Bug: v8:11231
Change-Id: I852d211227abacf867e8f1ab3e3ab06dbdba2a9b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2576006Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71765}