os: Import `path` automatically if available.

This matches CPython behavior:

```
>>> import os
>>> os.path.sep
'/'
```

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

python-stdlib/os/os/__init__.py

@@ -1,2 +1,8 @@
 # Replace built-in os module.
 from uos import *
+
+# Provide optional dependencies (which may be installed separately).
+try:
+    from . import path
+except ImportError:
+    pass