Add shiny.express.layout compatibility shim

Author: wch

shiny/express/layout.py

@@ -0,0 +1,14 @@
+import warnings
+
+from . import ui
+
+warnings.warn(
+    "shiny.express.layout has been deprecated and renamed to shiny.express.ui. "
+    "Please import shiny.express.ui instead of shiny.express.layout.",
+    ImportWarning,
+    stacklevel=2,
+)
+
+
+def __getattr__(name: str) -> object:
+    return getattr(ui, name)