Introduce custom gestures

These are gestures that aren't relevant globally but instead local.
The backend decides whether its gestures are custom or not.
It then has full responsibility to filter the correct gestures.

Author: leolost2605

lib/Gestures/Gesture.vala

@@ -47,6 +47,11 @@ namespace Gala {
     private class Gesture {
         public const float INVALID_COORD = float.MAX;
 
+        /**
+         * A hint that this gesture isn't a globally configured gesture but instead a local custom one.
+         * Examples for this are a scroll gesture on the workspaces or a scroll gesture to close windows.
+         */
+        public bool custom = false;
         public Clutter.EventType type;
         public GestureDirection direction;
         public int fingers;

lib/Gestures/GestureController.vala

@@ -158,7 +158,7 @@ public class Gala.GestureController : Object {
 
         var recognized_action = GestureSettings.get_action (gesture, out _action_info);
         recognizing = !wm.filter_action (recognized_action) && recognized_action == action ||
-            backend == scroll_backend && recognized_action == NONE;
+            recognized_action == CUSTOM;
 
         if (recognizing) {
             if (gesture.direction == UP || gesture.direction == RIGHT || gesture.direction == OUT) {

lib/Gestures/GestureSettings.vala

@@ -57,6 +57,11 @@ private class Gala.GestureSettings : Object {
 
     public static GestureAction get_action (Gesture gesture, out Variant? action_info = null) {
         action_info = null;
+
+        if (gesture.custom) {
+            return CUSTOM;
+        }
+
         var fingers = gesture.fingers;
 
         switch (gesture.type) {

lib/Gestures/ScrollBackend.vala

@@ -156,6 +156,7 @@ private class Gala.ScrollBackend : Object, GestureBackend {
         }
 
         return new Gesture () {
+            custom = true,
             type = Clutter.EventType.SCROLL,
             direction = direction,
             fingers = 2,