Add WebRTCIPPolicy setting to webContents and webview

Resolves #8777
Code to set and get the policy come from the muon framework code:
https://github.com/brave/muon/blob/master/atom/browser/api/atom_api_web_
contents.cc#L1324...L1343

lib/renderer/web-view/web-view-constants.js

@@ -20,6 +20,7 @@ module.exports = {
   ATTRIBUTE_GUESTINSTANCE: 'guestinstance',
   ATTRIBUTE_DISABLEGUESTRESIZE: 'disableguestresize',
   ATTRIBUTE_WEBPREFERENCES: 'webpreferences',
+  ATTRIBUTE_WEBRTCIPPOLICY: 'webrtcippolicy',
 
   // Internal attribute.
   ATTRIBUTE_INTERNALINSTANCEID: 'internalinstanceid',