[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/MecanumDriveKinematicsStructTest.cpp

@@ -0,0 +1,33 @@
+// 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/MecanumDriveKinematics.h"
+
+using namespace frc;
+
+namespace {
+
+using StructType = wpi::Struct<frc::MecanumDriveKinematics>;
+const MecanumDriveKinematics kExpectedData{MecanumDriveKinematics{
+    Translation2d{19.1_m, 2.2_m}, Translation2d{35.04_m, 1.91_m},
+    Translation2d{1.74_m, 3.504_m}, Translation2d{3.504_m, 1.91_m}}};
+}  // namespace
+
+TEST(MecanumDriveKinematicsStructTest, Roundtrip) {
+  uint8_t buffer[StructType::kSize];
+  std::memset(buffer, 0, StructType::kSize);
+  StructType::Pack(buffer, kExpectedData);
+
+  MecanumDriveKinematics unpacked_data = StructType::Unpack(buffer);
+
+  EXPECT_EQ(kExpectedData.GetFrontLeftWheel(),
+            unpacked_data.GetFrontLeftWheel());
+  EXPECT_EQ(kExpectedData.GetFrontRightWheel(),
+            unpacked_data.GetFrontRightWheel());
+  EXPECT_EQ(kExpectedData.GetRearLeftWheel(), unpacked_data.GetRearLeftWheel());
+  EXPECT_EQ(kExpectedData.GetRearRightWheel(),
+            unpacked_data.GetRearRightWheel());
+}