WIP: Bzlmod part the one hundred-seventeenth

Fix @rules_proto circular dep under WORKSPACE

Fixed by using `scala_proto_default_repositories` directly instead of
the `scala_proto_repositories` wrapper macro.

The problem was that `scala/private/macros/toolchains.bzl` had to load
`scala_proto/scala_proto.bzl` to get the previous macro definition. That
file defines `scala_proto_library` as a wrapper around a macro of the
same name from `scala_proto/private/scala_proto.bzl`. That file, in
turn, loads `@rules_proto//proto:defs.bzl`.

However, `scala_toolchains` from `scala/private/macros/toolchains.bzl`
is what now calls `scala_repositories`, which calls `rules_scala_setup`,
which instantiates the `rules_scala` repo. This wasn't a problem under
Bzlmod, but when building with `--noenable_bzlmod --enable_workspace`,
this happened:

```txt
ERROR: Failed to load Starlark extension
  '@@rules_proto//proto:repositories.bzl'.

Cycle in the workspace file detected.
  This indicates that a repository is used prior to being defined.

The following chain of repository dependencies lead to the missing definition.
 - @@rules_proto

This could either mean you have to add the '@@rules_proto' repository
  with a statement like `http_archive` in your WORKSPACE file
  (note that transitive dependencies are not added automatically),
  or move an existing definition earlier in your WORKSPACE file.

ERROR: Error computing the main repository mapping:
  cycles detected during computation of main repo mapping
```

Author: mbland

scala/private/macros/toolchains.bzl

@@ -10,7 +10,10 @@ load(
     "scalafmt_repositories",
 )
 load("//scala:scala_cross_version.bzl", "default_maven_server_urls")
-load("//scala_proto:scala_proto.bzl", "scala_proto_repositories")
+load(
+    "//scala_proto/default:repositories.bzl",
+    "scala_proto_default_repositories",
+)
 load("//scalatest:scalatest.bzl", "scalatest_repositories")
 load("//specs2:specs2_junit.bzl", "specs2_junit_repositories")
 load("//twitter_scrooge:twitter_scrooge.bzl", _scrooge = "twitter_scrooge")
@@ -131,7 +134,7 @@ def scala_toolchains(
             )
         if scala_proto:
             num_toolchains += 1
-            scala_proto_repositories(
+            scala_proto_default_repositories(
                 maven_servers = maven_servers,
                 scala_version = scala_version,
                 overriden_artifacts = overridden_artifacts,