- Add d8.file.read() and d8.file.execute() helpers
- Change tools and tests to use new d8.file helper
- Unify error throwing in v8::Shell::ReadFile

Change-Id: I5ef4cb27f217508a367106f01e872a4059d5e399
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2928505
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74883}