Move drag event to InputDispatcher (1/n)

This CL adds the ability to send a DRAG event through the
InputChannel, and adds the appropriate processing logic to
InputPublisher and InputConsumer.

Bug: 158242495
Test: atest libinput_tests InputPublisherAndConsumerTest
Change-Id: I7aead341a9851facf654024c476bd6d7eaae4590
diff --git a/include/android/input.h b/include/android/input.h
index 7973487..6fe95c0 100644
--- a/include/android/input.h
+++ b/include/android/input.h
@@ -166,6 +166,9 @@
 
     /** Capture event */
     AINPUT_EVENT_TYPE_CAPTURE = 4,
+
+    /** Drag event */
+    AINPUT_EVENT_TYPE_DRAG = 5,
 };
 
 /**