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/include/EventHub.h b/services/inputflinger/reader/include/EventHub.h
index 2a43466..c647558 100644
--- a/services/inputflinger/reader/include/EventHub.h
+++ b/services/inputflinger/reader/include/EventHub.h
@@ -71,18 +71,14 @@
 
 /* Describes an absolute axis. */
 struct RawAbsoluteAxisInfo {
-    bool valid{false}; // true if the information is valid, false otherwise
-
     int32_t minValue{};   // minimum value
     int32_t maxValue{};   // maximum value
     int32_t flat{};       // center flat position, eg. flat == 8 means center is between -8 and 8
     int32_t fuzz{};       // error tolerance, eg. fuzz == 4 means value is +/- 4 due to noise
     int32_t resolution{}; // resolution in units per mm or radians per mm
-
-    inline void clear() { *this = RawAbsoluteAxisInfo(); }
 };
 
-std::ostream& operator<<(std::ostream& out, const RawAbsoluteAxisInfo& info);
+std::ostream& operator<<(std::ostream& out, const std::optional<RawAbsoluteAxisInfo>& info);
 
 /*
  * Input device classes.