[Catalyst] Layer sidebar items are unresponsive on trailing edge

[ellbosch]

Repro by creating layers and attempting to select left-hand sidebar items on the trailing edge of the item view.

Catalyst appears to block all gestures on that trailing edge, as noted with the issue still existing when adjusting the size of the sidebar. I also confirmed with the view debugger that we are correctly using the full width of the view. The SwiftUI view uses the full space and the hosting controller's constraints adjust accordingly.