1. Skip leading zeros when parsing date string
2. Add necessary unittests

Bug: v8:12256
Change-Id: Ibc1f320382a2e33175f7f57542c8fe48afd05fa8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3223239Reviewed-by: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77592}