Report motion offsets for touchpad swipes

Adds two new axes, AXIS_GESTURE_X_OFFSET and AXIS_GESTURE_Y_OFFSET,
which report the movement of swipe gestures on the touchpad as a
fraction of the touchpad's size.

Bug: 246758376
Test: check axis values come through in a test app
Change-Id: I313410053a8db13273bd05a33d3a6a1f75081dae
diff --git a/include/android/input.h b/include/android/input.h
index d906af6..5d19c5c 100644
--- a/include/android/input.h
+++ b/include/android/input.h
@@ -771,6 +771,21 @@
      * The interpretation of a generic axis is device-specific.
      */
     AMOTION_EVENT_AXIS_GENERIC_16 = 47,
+    /**
+     * Axis constant: X gesture offset axis of a motion event.
+     *
+     * - For a touch pad, reports the distance that a swipe gesture has moved in the X axis, as a
+     *   proportion of the touch pad's size. For example, if a touch pad is 1000 units wide, and a
+     *   swipe gesture starts at X = 500 then moves to X = 400, this axis would have a value of
+     *   -0.1.
+     */
+    AMOTION_EVENT_AXIS_GESTURE_X_OFFSET = 48,
+    /**
+     * Axis constant: Y gesture offset axis of a motion event.
+     *
+     * The same as {@link AMOTION_EVENT_AXIS_GESTURE_X_OFFSET}, but for the Y axis.
+     */
+    AMOTION_EVENT_AXIS_GESTURE_Y_OFFSET = 49,
 
     /**
      * Note: This is not an "Axis constant". It does not represent any axis, nor should it be used
@@ -778,7 +793,7 @@
      * to make some computations (like iterating through all possible axes) cleaner.
      * Please update the value accordingly if you add a new axis.
      */
-    AMOTION_EVENT_MAXIMUM_VALID_AXIS_VALUE = AMOTION_EVENT_AXIS_GENERIC_16,
+    AMOTION_EVENT_MAXIMUM_VALID_AXIS_VALUE = AMOTION_EVENT_AXIS_GESTURE_Y_OFFSET,
 
     // NOTE: If you add a new axis here you must also add it to several other files.
     //       Refer to frameworks/base/core/java/android/view/MotionEvent.java for the full list.