Fix documentation warnings generated by JavaDoc (NFC) (#3428)

Some C++ Doxygen comments were updated to reflect any wording changes.

See `rg "(@return|@param \w+) TODO" | less` for list of incomplete docs.

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

@@ -96,6 +96,7 @@ public final class WPIMathJNI {
    *
    * @param path The path to the JSON.
    * @return A double array with the trajectory states from the JSON.
+   * @throws IOException if the JSON could not be read.
    */
   public static native double[] fromPathweaverJson(String path) throws IOException;
 
@@ -104,6 +105,7 @@ public final class WPIMathJNI {
    *
    * @param elements The elements of the trajectory.
    * @param path The location to save the JSON to.
+   * @throws IOException if the JSON could not be written.
    */
   public static native void toPathweaverJson(double[] elements, String path) throws IOException;