Introduce scrollEnabled property, refactor a way of setting the WebView settings, and apply minor fixes to the native codebase

[pklatka]

Summary

This PR:

1. Implements scrollEnabled property
2. Modifies the approach of applying the settings in the WebView
3. Applies minor fixes to the native codebase

Test plan

Tested if dynamically changing the scrollEnabled works properly in the demo app:

1. Tested if the prop is updated on the native side when on the same webpage (e.g. setTimeout which changes the value)
2. Tested if the changes are applied when going back to the previous screen

[pfeiffer]

Had a look at at least the iOS code and I'm wondering if a slightly different approach could be taken:

@objc var scrollEnabled {
  didSet {
    webView?.isScrollEnabled = scrollEnabled
  }
}

...

func visitableDidAppear(..) // or visitableDidRender? {
  webView?.isScrollEnabled = scrollEnabled
}

Could even be refactored to a method, eg configureWebView if we have a lot of options that need to be set on the WebView, eg.:

@objc var scrollEnabled {
  didSet {
     configureWebView()
  }
}

@objc var contentInset {
  didSet {
     configureWebView()
  }
}
...

func visitableDidAppear(..) // or visitableDidRender? {
  configureWebView()
}

func configureWebView() {
   guard webView != nil else { return }

   webView.isScrollEnabled = scrollEnabled
   webView.contentInset = contentInset
   ...
}