Add xml.__all__, remove import not existing at runtime (#13048)

stdlib/@tests/stubtest_allowlists/common.txt

@@ -591,8 +591,10 @@ email.mime
 email.parser
 email.quoprimime
 email.utils
+xml.__all__
 xml.dom
 xml.etree
+xml.parsers
 xml.sax
 
 # Missing aliases to existing methods that not many people seem to use.

stdlib/xml/__init__.pyi

@@ -1 +1,3 @@
-from xml import parsers as parsers
+# At runtime, listing submodules in __all__ without them being imported is
+# valid, and causes them to be included in a star import. See #6523
+__all__ = ["dom", "parsers", "sax", "etree"]  # noqa: F822  # pyright: ignore[reportUnsupportedDunderAll]