Add new `TouchpadInputMapper` class

This will replace `MultiTouchInputMapper` and `SingleTouchInputMapper`
for touchpad devices, and will be the wrapper for the gestures library.

Bug: 251196347
Test: connect Apple Magic Trackpad 2 to device, check logs come out
Test: atest inputflinger_tests
Change-Id: Ia8ee1779a40c6c6f98373e114c040bf13b7f213d
diff --git a/services/inputflinger/reader/include/EventHub.h b/services/inputflinger/reader/include/EventHub.h
index 8e5f15f..42ca482 100644
--- a/services/inputflinger/reader/include/EventHub.h
+++ b/services/inputflinger/reader/include/EventHub.h
@@ -94,7 +94,7 @@
     /* The input device is a cursor device such as a trackball or mouse. */
     CURSOR = 0x00000008,
 
-    /* The input device is a multi-touch touchscreen. */
+    /* The input device is a multi-touch touchscreen or touchpad. */
     TOUCH_MT = 0x00000010,
 
     /* The input device is a directional pad (implies keyboard, has DPAD keys). */
@@ -130,6 +130,9 @@
     /* The input device has sysfs controllable lights */
     LIGHT = 0x00008000,
 
+    /* The input device is a touchpad, requiring an on-screen cursor. */
+    TOUCHPAD = 0x00010000,
+
     /* The input device is virtual (not a real device, not part of UI configuration). */
     VIRTUAL = 0x40000000,