[wpiutil] Change Struct to allow non-constexpr implementation (#5992)

This required changing the constant values (e.g. kSize) into functions
(e.g. GetSize()).

Fixed implementations of ForEachNested to be inline (as these are actually
templates).

Also added a ntcore Struct test.

wpimath/src/test/native/cpp/kinematics/struct/ChassisSpeedsStructTest.cpp

@@ -16,8 +16,8 @@ const ChassisSpeeds kExpectedData{
 }  // namespace
 
 TEST(ChassisSpeedsStructTest, Roundtrip) {
-  uint8_t buffer[StructType::kSize];
-  std::memset(buffer, 0, StructType::kSize);
+  uint8_t buffer[StructType::GetSize()];
+  std::memset(buffer, 0, StructType::GetSize());
   StructType::Pack(buffer, kExpectedData);
 
   ChassisSpeeds unpacked_data = StructType::Unpack(buffer);

wpimath/src/test/native/cpp/kinematics/struct/DifferentialDriveKinematicsStructTest.cpp

@@ -16,8 +16,8 @@ const DifferentialDriveKinematics kExpectedData{
 }  // namespace
 
 TEST(DifferentialDriveKinematicsStructTest, Roundtrip) {
-  uint8_t buffer[StructType::kSize];
-  std::memset(buffer, 0, StructType::kSize);
+  uint8_t buffer[StructType::GetSize()];
+  std::memset(buffer, 0, StructType::GetSize());
   StructType::Pack(buffer, kExpectedData);
 
   DifferentialDriveKinematics unpacked_data = StructType::Unpack(buffer);

wpimath/src/test/native/cpp/kinematics/struct/DifferentialDriveWheelSpeedsStructTest.cpp

@@ -16,8 +16,8 @@ const DifferentialDriveWheelSpeeds kExpectedData{
 }  // namespace
 
 TEST(DifferentialDriveWheelSpeedsStructTest, Roundtrip) {
-  uint8_t buffer[StructType::kSize];
-  std::memset(buffer, 0, StructType::kSize);
+  uint8_t buffer[StructType::GetSize()];
+  std::memset(buffer, 0, StructType::GetSize());
   StructType::Pack(buffer, kExpectedData);
 
   DifferentialDriveWheelSpeeds unpacked_data = StructType::Unpack(buffer);

wpimath/src/test/native/cpp/kinematics/struct/MecanumDriveKinematicsStructTest.cpp

@@ -17,8 +17,8 @@ const MecanumDriveKinematics kExpectedData{MecanumDriveKinematics{
 }  // namespace
 
 TEST(MecanumDriveKinematicsStructTest, Roundtrip) {
-  uint8_t buffer[StructType::kSize];
-  std::memset(buffer, 0, StructType::kSize);
+  uint8_t buffer[StructType::GetSize()];
+  std::memset(buffer, 0, StructType::GetSize());
   StructType::Pack(buffer, kExpectedData);
 
   MecanumDriveKinematics unpacked_data = StructType::Unpack(buffer);

wpimath/src/test/native/cpp/kinematics/struct/MecanumDriveWheelPositionsStructTest.cpp

@@ -16,8 +16,8 @@ const MecanumDriveWheelPositions kExpectedData{
 }  // namespace
 
 TEST(MecanumDriveWheelPositionsStructTest, Roundtrip) {
-  uint8_t buffer[StructType::kSize];
-  std::memset(buffer, 0, StructType::kSize);
+  uint8_t buffer[StructType::GetSize()];
+  std::memset(buffer, 0, StructType::GetSize());
   StructType::Pack(buffer, kExpectedData);
 
   MecanumDriveWheelPositions unpacked_data = StructType::Unpack(buffer);

wpimath/src/test/native/cpp/kinematics/struct/MecanumDriveWheelSpeedsStructTest.cpp

@@ -16,8 +16,8 @@ const MecanumDriveWheelSpeeds kExpectedData{
 }  // namespace
 
 TEST(MecanumDriveWheelSpeedsStructTest, Roundtrip) {
-  uint8_t buffer[StructType::kSize];
-  std::memset(buffer, 0, StructType::kSize);
+  uint8_t buffer[StructType::GetSize()];
+  std::memset(buffer, 0, StructType::GetSize());
   StructType::Pack(buffer, kExpectedData);
 
   MecanumDriveWheelSpeeds unpacked_data = StructType::Unpack(buffer);

wpimath/src/test/native/cpp/kinematics/struct/SwerveModulePositionStructTest.cpp

@@ -16,8 +16,8 @@ const SwerveModulePosition kExpectedData{
 }  // namespace
 
 TEST(SwerveModulePositionStructTest, Roundtrip) {
-  uint8_t buffer[StructType::kSize];
-  std::memset(buffer, 0, StructType::kSize);
+  uint8_t buffer[StructType::GetSize()];
+  std::memset(buffer, 0, StructType::GetSize());
   StructType::Pack(buffer, kExpectedData);
 
   SwerveModulePosition unpacked_data = StructType::Unpack(buffer);

wpimath/src/test/native/cpp/kinematics/struct/SwerveModuleStateStructTest.cpp

@@ -16,8 +16,8 @@ const SwerveModuleState kExpectedData{
 }  // namespace
 
 TEST(SwerveModuleStateStructTest, Roundtrip) {
-  uint8_t buffer[StructType::kSize];
-  std::memset(buffer, 0, StructType::kSize);
+  uint8_t buffer[StructType::GetSize()];
+  std::memset(buffer, 0, StructType::GetSize());
   StructType::Pack(buffer, kExpectedData);
 
   SwerveModuleState unpacked_data = StructType::Unpack(buffer);