Report three- and four-finger swipes

The dispatcher still needs to be modified to only dispatch these to
SysUI windows.

Bug: 251196347
Test: check events received by a custom tester app, and touches shown by
      pointer location overlay
Test: atest inputflinger_tests
Change-Id: I3a7211d4a67e6388231bef158d3748c2e72e128d
diff --git a/include/input/Input.h b/include/input/Input.h
index 1a35196..7e62ac0 100644
--- a/include/input/Input.h
+++ b/include/input/Input.h
@@ -302,6 +302,12 @@
      * The current gesture represents the user swiping with two fingers on a touchpad.
      */
     TWO_FINGER_SWIPE = AMOTION_EVENT_CLASSIFICATION_TWO_FINGER_SWIPE,
+    /**
+     * The current gesture represents the user swiping with three or more fingers on a touchpad.
+     * Unlike two-finger swipes, these are only to be handled by the system UI, which is why they
+     * have a separate constant from two-finger swipes.
+     */
+    MULTI_FINGER_SWIPE = AMOTION_EVENT_CLASSIFICATION_MULTI_FINGER_SWIPE,
 };
 
 /**