Similar to what we did for FunctionMirror before in
https://crrev.com/c/2887508, we also need to avoid running user
JavaScript for DateMirrors.

This also refactors the ToDateString logic a bit.

Fixed: chromium:1311613
Change-Id: I793b86106765550a9aa449f85f0766840081cc58
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3571896Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79821}