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/libs/input/Input.cpp b/libs/input/Input.cpp
index d893cb9..000775b 100644
--- a/libs/input/Input.cpp
+++ b/libs/input/Input.cpp
@@ -72,6 +72,8 @@
             return "DEEP_PRESS";
         case MotionClassification::TWO_FINGER_SWIPE:
             return "TWO_FINGER_SWIPE";
+        case MotionClassification::MULTI_FINGER_SWIPE:
+            return "MULTI_FINGER_SWIPE";
     }
 }