[wpimath] Add protobuf/struct for trivial types (#5935)

This implements de/serialization for the types that aren't templated (SwerveDriveKinematics) in C++ or where there is no trivial way to go round-trip (Splines) for the messages.

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

@@ -0,0 +1,27 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include <gtest/gtest.h>
+
+#include "frc/kinematics/SwerveModulePosition.h"
+
+using namespace frc;
+
+namespace {
+
+using StructType = wpi::Struct<frc::SwerveModulePosition>;
+const SwerveModulePosition kExpectedData{
+    SwerveModulePosition{3.504_m, Rotation2d{17.4_rad}}};
+}  // namespace
+
+TEST(SwerveModulePositionStructTest, Roundtrip) {
+  uint8_t buffer[StructType::kSize];
+  std::memset(buffer, 0, StructType::kSize);
+  StructType::Pack(buffer, kExpectedData);
+
+  SwerveModulePosition unpacked_data = StructType::Unpack(buffer);
+
+  EXPECT_EQ(kExpectedData.distance.value(), unpacked_data.distance.value());
+  EXPECT_EQ(kExpectedData.angle, unpacked_data.angle);
+}