Emit webview internal events

[blaind]

Tracking issue for webview internal event emitting implementation.

Available events:

• webkitgtk2:
  • Load Events: https://webkitgtk.org/reference/webkit2gtk/stable/WebKitWebView.html#WebKitLoadEvent
• webview2: https://docs.microsoft.com/en-us/microsoft-edge/webview2/reference/win32/icorewebview2?view=webview2-1.0.1072.54#summary