[wpimath] Increase constexpr support in geometry data types (#4231)

This uses std::is_constant_evaluated() to conditionally use the gcem library for constexpr calculations.

wpimath/src/main/native/include/frc/geometry/Pose2d.inc

@@ -0,0 +1,39 @@
+// 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.
+
+#pragma once
+
+#include <utility>
+
+#include "frc/geometry/Pose2d.h"
+#include "frc/geometry/Rotation2d.h"
+#include "units/length.h"
+
+namespace frc {
+
+constexpr Pose2d::Pose2d(Translation2d translation, Rotation2d rotation)
+    : m_translation(std::move(translation)), m_rotation(std::move(rotation)) {}
+
+constexpr Pose2d::Pose2d(units::meter_t x, units::meter_t y,
+                         Rotation2d rotation)
+    : m_translation(x, y), m_rotation(std::move(rotation)) {}
+
+constexpr Pose2d Pose2d::operator+(const Transform2d& other) const {
+  return TransformBy(other);
+}
+
+constexpr Pose2d Pose2d::operator*(double scalar) const {
+  return Pose2d{m_translation * scalar, m_rotation * scalar};
+}
+
+constexpr Pose2d Pose2d::operator/(double scalar) const {
+  return *this * (1.0 / scalar);
+}
+
+constexpr Pose2d Pose2d::TransformBy(const Transform2d& other) const {
+  return {m_translation + (other.Translation().RotateBy(m_rotation)),
+          m_rotation + other.Rotation()};
+}
+
+}  // namespace frc