Update ActionBar icon documentation

[lukashlobil]

This page https://docs.nativescript.org/angular/ui/action-bar.html (and also the vanillaJS one) has references to action bar's icons. The url for android drawables hasn't worked for some months (it is working now) and the enumeration for iOS isn't really helpful. It should either be updated to also contain the images or the link for iOS documentation should lead here instead. Thank you for consideration

[NickIliev]

The iOS link should lead to https://developer.apple.com/documentation/uikit/uibarbuttonsystemitem

[radeva]

The link is fixed in the above PR. The other requests seems like irrelevant for the time being.