Use rules_scala from the Bazel Central Registry (#390)

The Bazel module for `rules_scala` v7.0.0 is now available on the Bazel
Central Registry:

- https://registry.bazel.build/modules/rules_scala

Also:

- Removes our own `rules_scala` extensions and the patch for v6.6.0, 
  since they're no longer necessary for v7.0.0. Leaves 
  `scala/extensions/README.md` in their place.

- Demonstrates how to configure Scala version 2.13.16 for Bzlmod
  similarly to how the previous configuration for `rules_scala` v6.6.0.

Author: mbland

MODULE.bazel

@@ -153,13 +153,13 @@ rules_ts_ext = use_extension(
 rules_ts_ext.deps()
 use_repo(rules_ts_ext, "npm_typescript")
 
-bazel_dep(name = "rules_scala")
-archive_override(
-    module_name = "rules_scala",
-    sha256 = "a4700d6e6cdf13cf85e29029ec998e2ec3ba94791606ec83d2c96e3c5b0aebed",
-    strip_prefix = "rules_scala-7.0.0",
-    url = "https://github.com/bazelbuild/rules_scala/releases/download/v7.0.0/rules_scala-v7.0.0.tar.gz",
+bazel_dep(name = "rules_scala", version = "7.0.0")
+
+scala_config = use_extension(
+    "@rules_scala//scala/extensions:config.bzl",
+    "scala_config",
 )
+scala_config.settings(scala_version = "2.13.16")
 
 scala_deps = use_extension(
     "@rules_scala//scala/extensions:deps.bzl",

MODULE.bazel.lock

@@ -0,0 +1,42 @@
+# Former `rules_scala` module extensions directory
+
+We removed the [module extensions][] from this directory after the release of
+[rules_scala v7.0.0][], which supports [Bazel modules (a.k.a. Bzlmod)][Bzlmod]
+directly. We also removed the patch for `rules_scala` v6.6.0 from this
+directory's parent.
+
+[Migrating to Bazel Modules (a.k.a. Bzlmod) - Module Extensions][post] from the
+[EngFlow 'bzlmod' blog post series][series] describes the former extensions and
+their configuration in detail. You can also see the previous files in the git
+history at commit `79b5193`:
+
+- [MODULE.bazel](https://github.com/EngFlow/example/blob/79b51930e4629486462c0f9787a25d035b6c4450/MODULE.bazel#L167-L317)
+- [scala/extensions/config.bzl](https://github.com/EngFlow/example/blob/79b51930e4629486462c0f9787a25d035b6c4450/scala/extensions/config.bzl)
+- [scala/extensions/deps.bzl](https://github.com/EngFlow/example/blob/79b51930e4629486462c0f9787a25d035b6c4450/scala/extensions/deps.bzl)
+- [scala/rules_scala-6.6.0.patch](https://github.com/EngFlow/example/blob/79b51930e4629486462c0f9787a25d035b6c4450/scala/rules_scala-6.6.0.patch)
+
+You can view these files locally using:
+
+```txt
+git show 79b5193:MODULE.bazel
+git show 79b5193:scala/extensions/config.bzl
+git show 79b5193:scala/extensions/deps.bzl
+git show 79b5193:scala/rules_scala-6.6.0.patch
+```
+
+To see the content of the `scala/extensions` directory at that commit:
+
+```sh
+$ git show 79b5193:scala/extensions
+tree 79b5193:scala/extensions
+
+BUILD
+config.bzl
+deps.bzl
+```
+
+[Bzlmod]: https://bazel.build/external/module
+[module extensions]: https://bazel.build/external/extension
+[rules_scala v7.0.0]: https://github.com/bazel-contrib/rules_scala/releases/tag/v7.0.0
+[post]: https://blog.engflow.com/2025/01/16/migrating-to-bazel-modules-aka-bzlmod---module-extensions/
+[series]: https://blog.engflow.com/category/bzlmod/