FB21059465: NSScrollView horizontal floating subview does not respect insets

FB21059465.md

The horizontal floating subview, when added to the NSScrollView, like with the snippet below, erroneusly adds the top inset twice (see attached screenshot). The floating subviews container view is not located at the begining of the safe content, but instead is located lower. That is not happening for the vertical floating subview:

        let scrollView: NSScrollView = ...
        scrollView.automaticallyAdjustsContentInsets = true // default
        let subview = NSView(frame: CGRect(x: 0, y: 0, width: 20, height: 20))
        subview.wantsLayer = true
        subview.layer?.backgroundColor = NSColor.red.cgColor
        scrollView.addFloatingSubview(subview, for: .horizontal)

Please check attached Xcode project that reproduce the issue. The red rectangle on the view should be located at the same origin as the text view in its view hirarchy.