Fix widget initialization issue

Fix widgets not initializing properly when integrating with third-party libraries (such as `ipywidgets`)

Author: jescalada

plotly/basewidget.py

@@ -142,6 +142,11 @@ def __init__(
         # views of this widget
         self._view_count = 0
 
+        # Initialize widget layout and data for third-party widget integration
+        # -------------------------------------------------------------------- 
+        self._widget_layout = deepcopy(self._layout_obj._props)
+        self._widget_data = deepcopy(self._data)
+
     def show(self, *args, **kwargs):
         return self