Add stubs for importlib.(resources.)readers (#10928)

Co-authored-by: Sebastian Rittau <srittau@rittau.biz>

stdlib/VERSIONS

@@ -152,8 +152,10 @@ imp: 2.7-3.11
 importlib: 2.7-
 importlib.metadata: 3.8-
 importlib.metadata._meta: 3.10-
+importlib.readers: 3.10-
 importlib.resources: 3.7-
 importlib.resources.abc: 3.11-
+importlib.resources.readers: 3.11-
 inspect: 2.7-
 io: 2.7-
 ipaddress: 3.3-