Add a global reference to the Streamlit library

I noticed the Streamlit.setComponentValue() example
was no longer working. For some reason, in the latest
releases the Streamlit library is no longer in the
global namespace. This change adds it back to the
window namespace, so JsCode callbacks in Folium can
return values to Streamlit.

streamlit_folium/frontend/src/index.tsx

@@ -29,6 +29,7 @@ declare global {
     drawnItems: any
     feature_group: any
     layer_control: any
+    Streamlit: any
   }
 }
 
@@ -165,6 +166,7 @@ function getPixelatedStyles(pixelated: boolean) {
   `
   return styles
 }
+window.Streamlit = Streamlit;
 
 window.initComponent = (map: any, return_on_hover: boolean) => {
   map.on("click", onMapClick)