[wpimath] Add geometry classes for Rectangle2d and Ellipse2d (#6555)

Co-authored-by: Tyler Veness <calcmogul@gmail.com>

wpimath/src/test/native/cpp/geometry/struct/Rectangle2dStructTest.cpp

@@ -0,0 +1,28 @@
+// 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/geometry/Rectangle2d.h"
+
+using namespace frc;
+
+namespace {
+
+using StructType = wpi::Struct<frc::Rectangle2d>;
+const Rectangle2d kExpectedData{
+    Pose2d{Translation2d{0.191_m, 2.2_m}, Rotation2d{22.9_rad}}, 1.2_m, 2.3_m};
+}  // namespace
+
+TEST(Rectangle2dStructTest, Roundtrip) {
+  uint8_t buffer[StructType::GetSize()];
+  std::memset(buffer, 0, StructType::GetSize());
+  StructType::Pack(buffer, kExpectedData);
+
+  Rectangle2d unpacked_data = StructType::Unpack(buffer);
+
+  EXPECT_EQ(kExpectedData.Center(), unpacked_data.Center());
+  EXPECT_EQ(kExpectedData.XWidth(), unpacked_data.XWidth());
+  EXPECT_EQ(kExpectedData.YWidth(), unpacked_data.YWidth());
+}