[wpimath] Split WPIMathJNI into logical chunks (#5552)

This makes things easier to find, and speeds up compilation.

wpimath/src/main/native/cpp/jni/WPIMathJNI_StateSpaceUtil.cpp

@@ -0,0 +1,44 @@
+// 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 <jni.h>
+
+#include <Eigen/Core>
+#include <wpi/jni_util.h>
+
+#include "edu_wpi_first_math_WPIMathJNI.h"
+#include "frc/StateSpaceUtil.h"
+
+using namespace wpi::java;
+
+extern "C" {
+
+/*
+ * Class:     edu_wpi_first_math_WPIMathJNI
+ * Method:    isStabilizable
+ * Signature: (II[D[D)Z
+ */
+JNIEXPORT jboolean JNICALL
+Java_edu_wpi_first_math_WPIMathJNI_isStabilizable
+  (JNIEnv* env, jclass, jint states, jint inputs, jdoubleArray aSrc,
+   jdoubleArray bSrc)
+{
+  JSpan<const jdouble> nativeA{env, aSrc};
+  JSpan<const jdouble> nativeB{env, bSrc};
+
+  Eigen::Map<const Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic,
+                                 Eigen::RowMajor>>
+      A{nativeA.data(), states, states};
+
+  Eigen::Map<const Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic,
+                                 Eigen::RowMajor>>
+      B{nativeB.data(), states, inputs};
+
+  bool isStabilizable =
+      frc::IsStabilizable<Eigen::Dynamic, Eigen::Dynamic>(A, B);
+
+  return isStabilizable;
+}
+
+}  // extern "C"