[wpimath] Use JNI for trajectory serialization (#3257)

wpimath/src/main/java/edu/wpi/first/math/WPIMathJNI.java

@@ -91,6 +91,38 @@ public final class WPIMathJNI {
    */
   public static native boolean isStabilizable(int states, int inputs, double[] A, double[] B);
 
+  /**
+   * Loads a Pathweaver JSON.
+   *
+   * @param path The path to the JSON.
+   * @return A double array with the trajectory states from the JSON.
+   */
+  public static native double[] fromPathweaverJson(String path) throws IOException;
+
+  /**
+   * Converts a trajectory into a Pathweaver JSON and saves it.
+   *
+   * @param elements The elements of the trajectory.
+   * @param path The location to save the JSON to.
+   */
+  public static native void toPathweaverJson(double[] elements, String path) throws IOException;
+
+  /**
+   * Deserializes a trajectory JSON into a double[] of trajectory elements.
+   *
+   * @param json The JSON containing the serialized trajectory.
+   * @return A double array with the trajectory states.
+   */
+  public static native double[] deserializeTrajectory(String json);
+
+  /**
+   * Serializes the trajectory into a JSON string.
+   *
+   * @param elements The elements of the trajectory.
+   * @return A JSON containing the serialized trajectory.
+   */
+  public static native String serializeTrajectory(double[] elements);
+
   public static class Helper {
     private static AtomicBoolean extractOnStaticLoad = new AtomicBoolean(true);