Add stub @rules_python to third_party/
This stub contains only one relevant file, @rules_python//python:defs.bzl,
which mimics the file at the same path in bazelbuild/rules_python. Having this
repo gives us a way to inject this defs.bzl file into our protobuf dependency,
which is loaded as a separate (local) external repo and therefore cannot access
the existing //tools/python:private/defs.bzl in Bazel's own workspace. It also
means we'll be compatible with the future upstream migration to fix protobuf
for #9006.
A separate PR will add this to the Bazel root WORKSPACE file (since
third_party/ must be updated in a separate commit).
Break-out of #9019. Work toward #9006.
Closes #9044.
RELNOTES: None
diff --git a/third_party/rules_python/rules_python.WORKSPACE b/third_party/rules_python/rules_python.WORKSPACE
new file mode 100644
index 0000000..96961d9
--- /dev/null
+++ b/third_party/rules_python/rules_python.WORKSPACE
@@ -0,0 +1,7 @@
+# A stub version of bazelbuild/rules_python that contains only the defs.bzl
+# file, which is needed to access native Python rules under
+# --incompatible_load_python_rules_from_bzl (#9006).
+#
+# TODO(#9029): Maybe replace this with the real thing.
+
+workspace(name = "rules_python")
