Feature: accessibility tab order

[m-abs]

We should be able to set the tab ordering for accessible elements in NativeScript

On iOS we have UIAccessibilityContainer

On Android the View have these properties:
android:nextFocusUp, android:nextFocusDown, android:nextFocusLeft, and android:nextFocusRight,
https://developer.android.com/reference/android/view/View.html#attr_android:nextFocusUp