Add InputReaderConfiguration option for touchpad visualization

Test: Enable the flag and enable the "Show touchpad input" in developer
      options and trace the logs in TouchpadInputMapper.
Bug: 286551975
Flag: com.android.hardware.input.touchpad_visualizer
Change-Id: Ibe8bdae8757391501eb66753d53b046011d1da45
diff --git a/services/inputflinger/reader/mapper/TouchpadInputMapper.h b/services/inputflinger/reader/mapper/TouchpadInputMapper.h
index 8baa63e..4856fe0 100644
--- a/services/inputflinger/reader/mapper/TouchpadInputMapper.h
+++ b/services/inputflinger/reader/mapper/TouchpadInputMapper.h
@@ -112,6 +112,10 @@
     std::optional<ui::LogicalDisplayId> mDisplayId;
 
     nsecs_t mGestureStartTime{0};
+
+    // True if hardware state update notifications is available for usage based on its feature flag
+    // and settings value.
+    bool mTouchpadHardwareStateNotificationsEnabled = false;
 };
 
 } // namespace android