Add UIGestureRecognizerDelegate and PanGestureRecogniser (#3597)

- Allow all gestures simultaneously recognized.
- Add PanGestureRecogniser with min/max number of touches.
- Fix sending delta values relative to Update instead to match macOS.
- Fix rotation gesture units from iOS to be in degrees instead of radians.

Co-authored-by: Mads Marquart <mads@marquart.dk>

src/event.rs

@@ -293,6 +293,19 @@ pub enum WindowEvent {
         phase: TouchPhase,
     },
 
+    /// N-finger pan gesture
+    ///
+    /// ## Platform-specific
+    ///
+    /// - Only available on **iOS**.
+    /// - On iOS, not recognized by default. It must be enabled when needed.
+    PanGesture {
+        device_id: DeviceId,
+        /// Change in pixels of pan gesture from last update.
+        delta: PhysicalPosition<f32>,
+        phase: TouchPhase,
+    },
+
     /// Double tap gesture.
     ///
     /// On a Mac, smart magnification is triggered by a double tap with two fingers
@@ -322,7 +335,12 @@ pub enum WindowEvent {
     ///
     /// - Only available on **macOS** and **iOS**.
     /// - On iOS, not recognized by default. It must be enabled when needed.
-    RotationGesture { device_id: DeviceId, delta: f32, phase: TouchPhase },
+    RotationGesture {
+        device_id: DeviceId,
+        /// change in rotation in degrees
+        delta: f32,
+        phase: TouchPhase,
+    },
 
     /// Touchpad pressure event.
     ///
@@ -993,6 +1011,7 @@ impl PartialEq for InnerSizeWriter {
 
 #[cfg(test)]
 mod tests {
+    use crate::dpi::PhysicalPosition;
     use crate::event;
     use std::collections::{BTreeSet, HashSet};
 
@@ -1055,6 +1074,11 @@ mod tests {
                     delta: 0.0,
                     phase: event::TouchPhase::Started,
                 });
+                with_window_event(PanGesture {
+                    device_id: did,
+                    delta: PhysicalPosition::<f32>::new(0.0, 0.0),
+                    phase: event::TouchPhase::Started,
+                });
                 with_window_event(TouchpadPressure { device_id: did, pressure: 0.0, stage: 0 });
                 with_window_event(AxisMotion { device_id: did, axis: 0, value: 0.0 });
                 with_window_event(Touch(event::Touch {