TouchEvent (1/n): Adding TouchModeEvent to InputChannel

This CL detaches the touch mode state update from focus update. It does
that by introducing a new internal event (TouchModeEvent). This CL also
adds this event to InputChannel and related processing logic to
InputPublisher and InputConsumer. InputDispatcher will process two
different events now: FocusEvent when gaining/losing focus and
TouchModeEvent when entering/leaving touch mode.

Test: atest libinput_tests
Bug: 193718270
Change-Id: Ie4e5b6e8e798f12d7203127b4559fa40d38788de
diff --git a/include/android/input.h b/include/android/input.h
index bb98beb..f03facb 100644
--- a/include/android/input.h
+++ b/include/android/input.h
@@ -169,6 +169,9 @@
 
     /** Drag event */
     AINPUT_EVENT_TYPE_DRAG = 5,
+
+    /** TouchMode event */
+    AINPUT_EVENT_TYPE_TOUCH_MODE = 6,
 };
 
 /**