The `Script::source_url` field holds the value of the magic
`//# sourceURL` comment if found, and the `Script::name` field is
supposed to hold the actual name of the resource (as provided by
the embedder ideally), in case of Chromium that's supposed to be
the URL (in case of Node.js it's often the local path).

Using `source_url` worked by chance so far, but for loading DWARF
symbol files correctly we need the initiator (which we pick from
the embedderName of the Script as reported to DevTools). More
importantly, the partial handling of `//# sourceURL` in V8 is a
layering violation and causes trouble in DevTools, i.e. when users
put relative paths here. So as part of refactoring and correctifying
the handling of `//# sourceURL`, we need to make sure that the embedder
provided name (the URL in case of Chromium) is always stored in the
`Script::name` field.

Bug: chromium:1183990, chromium:974543, chromium:1174507
Change-Id: I32e11def2b9b52be11bd2e0e64a2ab6bdcf5e52d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2773584
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73536}