Fix floating panel content view constraints (scenee#546)

See https://stackoverflow.com/questions/58399123/uihostingcontroller-should-expand-to-fit-contents

Author: seanlh

Examples/Maps-SwiftUI/Maps/FloatingPanel/FloatingPanelView.swift

@@ -98,6 +98,10 @@ struct FloatingPanelView<Content: View, FloatingPanelContent: View>: UIViewContr
             hostingViewController.view.backgroundColor = nil
             fpc.set(contentViewController: hostingViewController)
             fpc.addPanel(toParent: parentViewController, at: 1, animated: false)
+            
+            // Invalidate the UIHostingController's intrinsic content size
+            // as it did not yet know the floating panel constraints.
+            contentViewController?.view?.invalidateIntrinsicContentSize()
         }
 
         func updateIfNeeded() {