InputDevice: return std::optional from getAbsoluteAxisInfo

This also allows us to remove the valid field from RawAbsoluteAxisInfo,
since we can represent "invalid" axes (which usually just meant absent
ones) using std::nullopt.

Test: atest inputflinger_tests
Test: m checkinput
Test: Check "Raw Touch Axes" section of touch input mapper info in
      dumpsys input
Bug: 245989146
Flag: EXEMPT refactor
Change-Id: I045a2e0b61a84657f2f8171c1fee3cc3e331ac86
diff --git a/services/inputflinger/reader/mapper/ExternalStylusInputMapper.h b/services/inputflinger/reader/mapper/ExternalStylusInputMapper.h
index c040a7b..d48fd9b 100644
--- a/services/inputflinger/reader/mapper/ExternalStylusInputMapper.h
+++ b/services/inputflinger/reader/mapper/ExternalStylusInputMapper.h
@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <optional>
+
 #include "InputMapper.h"
 
 #include "SingleTouchMotionAccumulator.h"
@@ -43,7 +45,7 @@
 
 private:
     SingleTouchMotionAccumulator mSingleTouchMotionAccumulator;
-    RawAbsoluteAxisInfo mRawPressureAxis;
+    std::optional<RawAbsoluteAxisInfo> mRawPressureAxis;
     TouchButtonAccumulator mTouchButtonAccumulator;
 
     StylusState mStylusState;