gh-90473: Skip and document more failing tests on WASI (GH-93436)

- Mark more ``umask()`` cases
- ``dup()`` is not supported
- ``/dev/null`` is not available
- document missing features
- mark more modules as not available

Lib/test/test_pathlib.py

@@ -2353,6 +2353,9 @@ class _BasePathTest(object):
     @unittest.skipIf(
         is_emscripten, "Unix sockets are not implemented on Emscripten."
     )
+    @unittest.skipIf(
+        is_wasi, "Cannot create socket on WASI."
+    )
     def test_is_socket_true(self):
         P = self.cls(BASE, 'mysock')
         sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)