[upstream_utils] Update to latest Eigen HEAD (#5996)

There hasn't been a release in 2.5 years.

There's performance improvements for some NEON instructions, UB fixes, a lot of internal cleanup with the jump from C++11 to C++14, and more constexpr.

wpimath/src/main/native/thirdparty/eigen/include/Eigen/Eigenvalues

@@ -19,20 +19,22 @@
 #include "src/Core/util/DisableStupidWarnings.h"
 
 /** \defgroup Eigenvalues_Module Eigenvalues module
-  *
-  *
-  *
-  * This module mainly provides various eigenvalue solvers.
-  * This module also provides some MatrixBase methods, including:
-  *  - MatrixBase::eigenvalues(),
-  *  - MatrixBase::operatorNorm()
-  *
-  * \code
-  * #include <Eigen/Eigenvalues>
-  * \endcode
-  */
+ *
+ *
+ *
+ * This module mainly provides various eigenvalue solvers.
+ * This module also provides some MatrixBase methods, including:
+ *  - MatrixBase::eigenvalues(),
+ *  - MatrixBase::operatorNorm()
+ *
+ * \code
+ * #include <Eigen/Eigenvalues>
+ * \endcode
+ */
 
 #include "src/misc/RealSvd2x2.h"
+
+// IWYU pragma: begin_exports
 #include "src/Eigenvalues/Tridiagonalization.h"
 #include "src/Eigenvalues/RealSchur.h"
 #include "src/Eigenvalues/EigenSolver.h"
@@ -54,7 +56,8 @@
 // #include "src/Eigenvalues/ComplexSchur_LAPACKE.h"
 // #include "src/Eigenvalues/SelfAdjointEigenSolver_LAPACKE.h"
 #endif
+// IWYU pragma: end_exports
 
 #include "src/Core/util/ReenableStupidWarnings.h"
 
-#endif // EIGEN_EIGENVALUES_MODULE_H
+#endif  // EIGEN_EIGENVALUES_MODULE_H