This essentially allows to pass both user and email, so that we can
either prefer the user to retrieve the avatar or (if user is not
present) fall back to the email lookup.

We want to drop the generic #avatar_icon helper that supports both an email
and a user object being passed in. Instead, we want to explicitly use the #avatar_icon_for_user
and #avatar_icon_for_email helpers depending on what we have at hand.
This allows us to avoid unnecessary database queries (e.g. call
User.find_by_any_email if we already have the user).

In situations like here, this makes it less convenient to use.

Whenever we already deal with a User object, let's use the more specific
method avatar_icon_for_user.

When we don't use the original `ApplicationHelper#avatar_icon` anymore, we
can just remove it (and its specs).

Closes #42800.

The refs hash is used to determine what branches and tags have a commit
as head in the network graph. The previous implementation depended on
Rugged#references. The problem with this implementation was that it
depended on rugged, but also that it iterated over all references and
thus loading more data than needed if for example the project uses CI/CD
environments, Pipelines, or Merge Requests.

Given only refs are checked the network cares about the GraphHelper#refs
method has no need to reject those, simplifying the method.

Closes gitlab-org/gitaly#880

From https://gitlab.com/gitlab-org/gitlab-ce/issues/36760

Was reverted in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14373

Callers expect a URL.

This fixes the avatars in commit lists when a user has no avatar and
Gravatar is disabled.

Closes #38715

fix bug in webpack_helper in which force_same_domain argument was ignored breaking local rspec tests