This CL updates Realm.eval() to also handle reading source code as a
JavaScript function or from a file. To distinguish between different
argument types, an additional options bag needs to be provided. If no
options bag is provided, the behavior defaults to the current one,
which is reading source code from a string.

Bug: v8:11525, v8:11706
Change-Id: I68238335eb91171041dca2c83db211c40dd68359
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2944435Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Vicky Kontoura <vkont@google.com>
Cr-Commit-Position: refs/heads/master@{#75021}