NEW: Expose displayIndex via the Touch object (#1677)

* Recreate change from Tony for touch displayIndex support

Author: stefanunity

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -14,6 +14,7 @@ however, it has to be formatted properly to pass verification tests.
 - Added `InputSystem.customBindingPathValidators` interface to allow showing warnings in the `InputAsset` Editor for specific InputBindings and draw custom UI in the properties panel.
 - Added `InputSystem.runInBackground` to be used internally by specific platforms packages. Allows telling the input system that a specific platform runs in background. It allows fixing of [case UUM-6744](https://issuetracker.unity3d.com/product/unity/issues/guid/UUM-6744).
 - Added new UIToolkit version of the `InputActionsAsset` editor. Currently this is incomplete (view-only) and the existing editor is still used by default.
+- Added `displayIndex` field to the Touch struct to expose the index of the display that was touched.
 
 ### Changed
 - Changed XR Layout build behavior to create Axis2D control devices with `StickControl` type instead of `Vector2Control`.

Packages/com.unity.inputsystem/InputSystem/Plugins/EnhancedTouch/Touch.cs

@@ -235,6 +235,14 @@ public struct Touch : IEquatable<Touch>
         /// <seealso cref="TouchControl.tap"/>
         public bool isTap => state.isTap;
 
+        /// <summary>
+        /// The index of the display containing the touch.
+        /// </summary>
+        /// <value>A zero based number representing the display index containing the touch.</value>
+        /// <seealso cref="TouchControl.displayIndex"/>
+        /// <seealso cref="Display"/>
+        public int displayIndex => state.displayIndex;
+
         /// <summary>
         /// Whether the touch is currently in progress, i.e. has a <see cref="phase"/> of
         /// <see cref="TouchPhase.Began"/>, <see cref="TouchPhase.Moved"/>, or <see cref="TouchPhase.Stationary"/>.