[wpimath] Add Sleipnir (#6541)

This is useful for solving quadratic programs.

wpimath/src/test/native/cpp/SleipnirTest.cpp

@@ -0,0 +1,26 @@
+// 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 <sleipnir/optimization/OptimizationProblem.hpp>
+
+TEST(SleipnirTest, Quartic) {
+  sleipnir::OptimizationProblem problem;
+
+  auto x = problem.DecisionVariable();
+  x.SetValue(20.0);
+
+  problem.Minimize(sleipnir::pow(x, 4));
+
+  problem.SubjectTo(x >= 1);
+
+  auto status = problem.Solve({.diagnostics = true});
+
+  EXPECT_EQ(status.costFunctionType, sleipnir::ExpressionType::kNonlinear);
+  EXPECT_EQ(status.equalityConstraintType, sleipnir::ExpressionType::kNone);
+  EXPECT_EQ(status.inequalityConstraintType, sleipnir::ExpressionType::kLinear);
+  EXPECT_EQ(status.exitCondition, sleipnir::SolverExitCondition::kSuccess);
+
+  EXPECT_NEAR(x.Value(), 1.0, 1e-6);
+}