Minor scroll gesture recognizer fixes

src/Avalonia.Base/Input/GestureRecognizers/ScrollGestureRecognizer.cs

@@ -66,8 +66,7 @@ namespace Avalonia.Input.GestureRecognizers
         
         public void PointerPressed(PointerPressedEventArgs e)
         {
-            if (e.Pointer.IsPrimary && 
-                (e.Pointer.Type == PointerType.Touch || e.Pointer.Type == PointerType.Pen))
+            if (e.Pointer.Type == PointerType.Touch || e.Pointer.Type == PointerType.Pen)
             {
                 EndGesture();
                 _tracking = e.Pointer;

src/Avalonia.Base/Input/Raw/RawPointerEventArgs.cs

@@ -137,9 +137,13 @@ namespace Avalonia.Input.Raw
         /// </summary>
         public Point Position { get; set; }
 
+        /// <inheritdoc cref="PointerPointProperties.Twist" />
         public float Twist { get; set; }
+        /// <inheritdoc cref="PointerPointProperties.Pressure" />
         public float Pressure { get; set; }
+        /// <inheritdoc cref="PointerPointProperties.XTilt" />
         public float XTilt { get; set; }
+        /// <inheritdoc cref="PointerPointProperties.YTilt" />
         public float YTilt { get; set; }