isAccessibilityElement should not return false for NSUIView

[becknaum]

Since isAccessibilityElement is a final, overridden property of NSUIView in Platform+Accessibility.swift, it is essentially read-only, since the setter has no effect. The comment explains that it is to make children accessible, but this is something that should be configurable since UIView allows it. The use case I am running into is that the chart data is repeated in another format within the same view, rendering the chart data redundant to a voiceover listener. The chart is purely a visual aid in this case.