Add regrtest from CPython

Author: palaviv

Lib/test/libregrtest/__init__.py

@@ -0,0 +1,5 @@
+# We import importlib *ASAP* in order to test #15386
+import importlib
+
+from test.libregrtest.cmdline import _parse_args, RESOURCE_NAMES, ALL_RESOURCES
+from test.libregrtest.main import main