Use TWO_FINGER_SWIPE classification for touchpad scroll events

This allows apps to distinguish the fake finger created for touchpad
scrolling from an actual finger.

Bug: 246758376
Test: add classification to InputDispatcher's outbound event logs and
      check the new value is used when scrolling
Change-Id: Ia90f9984e75ad6fde2d0e42628ab42eab371b7a5
diff --git a/libs/input/Input.cpp b/libs/input/Input.cpp
index 2b7483d..579b28e 100644
--- a/libs/input/Input.cpp
+++ b/libs/input/Input.cpp
@@ -87,6 +87,8 @@
             return "AMBIGUOUS_GESTURE";
         case MotionClassification::DEEP_PRESS:
             return "DEEP_PRESS";
+        case MotionClassification::TWO_FINGER_SWIPE:
+            return "TWO_FINGER_SWIPE";
     }
 }