python: Enable Starlark implementation of Python rules

This enables the Starlark implementation of the Python rules. While these are
largely drop-in replacements, there are a handful of edge cases that
are known to be incompatible; see #15897
for the list of cases.

If you believe the Starlark implementation to be the cause of a problem, please
post to #15897.

Work towards #15897

PiperOrigin-RevId: 509295132
Change-Id: Icbe5beb32e0700a915ac40fe4dbcacf102382974

src/main/starlark/builtins_bzl/bazel/exports.bzl

@@ -32,8 +32,8 @@ exported_rules = {
     "java_proto_library": java_proto_library,
     "+cc_proto_library": cc_proto_library,
     "+java_binary": java_binary,
-    "-py_binary": py_binary,
-    "-py_test": py_test,
-    "-py_library": py_library,
+    "+py_binary": py_binary,
+    "+py_test": py_test,
+    "+py_library": py_library,
 }
 exported_to_java = {}