Gazelle:resolve support bzlmod repo canonical name

[sluongng]

More details of what I am attempting could be found in bazelbuild/bazel#19301

Given a bzlmod directive like this

go_deps.gazelle_override(
    directives = ["gazelle:resolve go github.com/some/path @@//my/target"],
    path = "github.com/foo/bar",
)

The BUILD file would be generated with @//my/target instead of @@//my/target.

This unfortunately make it harder for us to overcome the issue linked above.

The current workaround is to use a patch file instead of gazelle directives, it would be nice if Gazelle could accept @@ as the repo name.

[fmeum]

We generally don't want Gazelle to emit canonical repository names into BUILD files at all as that can break strict deps and go unnoticed for a long time.

I see how this would allow a less tedious workaround for the linked Bazel issue, but I would strongly prefer just fixing that issue soon instead (say for 7.2.0 at the latest).