Vendor dependencies

Let's see how I like this workflow.

vendor/cxx/tools/buck/prelude/test_suite.bzl

@@ -0,0 +1,11 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under both the MIT license found in the
+# LICENSE-MIT file in the root directory of this source tree and the Apache
+# License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+# of this source tree.
+
+def test_suite_impl(_ctx: "context") -> ["provider"]:
+    # There is nothing to implement here: test_suite exists as a mechanism to "group" tests using
+    # the `tests` attribute, and the `tests` attribute is supported for all rules.
+    return [DefaultInfo()]