Fix the event handling on presentation modally

If an alpha of the controller's backdrop view is zero, the presentation controller
must not block any touch event outside of surface view.

Framework/Sources/FloatingPanelTransitioning.swift

@@ -59,6 +59,8 @@ class FloatingPanelPresentationController: UIPresentationController {
             fpView.bottomAnchor.constraint(equalTo: containerView.bottomAnchor, constant: 0.0),
             ])
 
+        (fpView as? FloatingPanelPassThroughView)?.eventForwardingView = presentingViewController.view
+
         let tapGesture = UITapGestureRecognizer(target: self, action: #selector(handleBackdrop(tapGesture:)))
         fpc.backdropView.addGestureRecognizer(tapGesture)
     }

Framework/Sources/FloatingPanelView.swift

@@ -6,13 +6,14 @@
 import UIKit
 
 class FloatingPanelPassThroughView: UIView {
+    public weak var eventForwardingView: UIView?
     public override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
-        let view = super.hitTest(point, with: event)
-        switch view {
-        case is FloatingPanelPassThroughView:
-            return nil
+        let hitView = super.hitTest(point, with: event)
+        switch hitView {
+        case self:
+            return eventForwardingView?.hitTest(self.convert(point, to: eventForwardingView), with: event)
         default:
-            return view
+            return hitView
         }
     }
 }