Add isjunction and splitroot functions (#10642)

stdlib/ntpath.pyi

@@ -42,6 +42,9 @@ from posixpath import (
     splitext as splitext,
     supports_unicode_filenames as supports_unicode_filenames,
 )
+
+if sys.version_info >= (3, 12):
+    from posixpath import isjunction as isjunction, splitroot as splitroot
 from typing import AnyStr, overload
 from typing_extensions import LiteralString
 
@@ -85,6 +88,8 @@ __all__ = [
     "samestat",
     "commonpath",
 ]
+if sys.version_info >= (3, 12):
+    __all__ += ["isjunction", "splitroot"]
 
 altsep: LiteralString