feat(events): Add isTopFrame to shouldStartLoadForRequest (#1537)
* Add isTopFrame to shouldStartLoadForRequest on iOS
onLoadingStart is not raised for inner frames, but onShouldStartLoadWithRequest still is. This keeps that behavior but adds isTopFrame to onShouldStartLoadWithRequest so that apps can perform their own filtering if desired.
* Update docs
Co-authored-by: Jamon Holmgren <jamonholmgren@gmail.com>