[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/main/native/cpp/controller/proto/ArmFeedforwardProto.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 "frc/controller/proto/ArmFeedforwardProto.h"
+
+#include "controller.pb.h"
+
+google::protobuf::Message* wpi::Protobuf<frc::ArmFeedforward>::New(
+    google::protobuf::Arena* arena) {
+  return google::protobuf::Arena::CreateMessage<
+      wpi::proto::ProtobufArmFeedforward>(arena);
+}
+
+frc::ArmFeedforward wpi::Protobuf<frc::ArmFeedforward>::Unpack(
+    const google::protobuf::Message& msg) {
+  auto m = static_cast<const wpi::proto::ProtobufArmFeedforward*>(&msg);
+  return frc::ArmFeedforward{
+      units::volt_t{m->ks()},
+      units::volt_t{m->kg()},
+      units::unit_t<frc::ArmFeedforward::kv_unit>{m->kv()},
+      units::unit_t<frc::ArmFeedforward::ka_unit>{m->ka()},
+  };
+}
+
+void wpi::Protobuf<frc::ArmFeedforward>::Pack(
+    google::protobuf::Message* msg, const frc::ArmFeedforward& value) {
+  auto m = static_cast<wpi::proto::ProtobufArmFeedforward*>(msg);
+  m->set_ks(value.kS.value());
+  m->set_kg(value.kG.value());
+  m->set_kv(value.kV.value());
+  m->set_ka(value.kA.value());
+}

wpimath/src/main/native/cpp/controller/proto/DifferentialDriveWheelVoltagesProto.cpp

@@ -0,0 +1,34 @@
+// 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 "frc/controller/proto/DifferentialDriveWheelVoltagesProto.h"
+
+#include "controller.pb.h"
+
+google::protobuf::Message* wpi::Protobuf<
+    frc::DifferentialDriveWheelVoltages>::New(google::protobuf::Arena* arena) {
+  return google::protobuf::Arena::CreateMessage<
+      wpi::proto::ProtobufDifferentialDriveWheelVoltages>(arena);
+}
+
+frc::DifferentialDriveWheelVoltages
+wpi::Protobuf<frc::DifferentialDriveWheelVoltages>::Unpack(
+    const google::protobuf::Message& msg) {
+  auto m =
+      static_cast<const wpi::proto::ProtobufDifferentialDriveWheelVoltages*>(
+          &msg);
+  return frc::DifferentialDriveWheelVoltages{
+      units::volt_t{m->left()},
+      units::volt_t{m->right()},
+  };
+}
+
+void wpi::Protobuf<frc::DifferentialDriveWheelVoltages>::Pack(
+    google::protobuf::Message* msg,
+    const frc::DifferentialDriveWheelVoltages& value) {
+  auto m =
+      static_cast<wpi::proto::ProtobufDifferentialDriveWheelVoltages*>(msg);
+  m->set_left(value.left.value());
+  m->set_right(value.right.value());
+}

wpimath/src/main/native/cpp/controller/proto/ElevatorFeedforwardProto.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 "frc/controller/proto/ElevatorFeedforwardProto.h"
+
+#include "controller.pb.h"
+
+google::protobuf::Message* wpi::Protobuf<frc::ElevatorFeedforward>::New(
+    google::protobuf::Arena* arena) {
+  return google::protobuf::Arena::CreateMessage<
+      wpi::proto::ProtobufElevatorFeedforward>(arena);
+}
+
+frc::ElevatorFeedforward wpi::Protobuf<frc::ElevatorFeedforward>::Unpack(
+    const google::protobuf::Message& msg) {
+  auto m = static_cast<const wpi::proto::ProtobufElevatorFeedforward*>(&msg);
+  return frc::ElevatorFeedforward{
+      units::volt_t{m->ks()},
+      units::volt_t{m->kg()},
+      units::unit_t<frc::ElevatorFeedforward::kv_unit>{m->kv()},
+      units::unit_t<frc::ElevatorFeedforward::ka_unit>{m->ka()},
+  };
+}
+
+void wpi::Protobuf<frc::ElevatorFeedforward>::Pack(
+    google::protobuf::Message* msg, const frc::ElevatorFeedforward& value) {
+  auto m = static_cast<wpi::proto::ProtobufElevatorFeedforward*>(msg);
+  m->set_ks(value.kS());
+  m->set_kg(value.kG());
+  m->set_kv(value.kV());
+  m->set_ka(value.kA());
+}