[docs] Set Doxygen extract_all to true and fix Doxygen failures (#3695)

The template argument order for UnscentedTransform was reversed to match
all the other UKF classes. Since UnscentedTransform is intended as a
class for internal use only, this shouldn't cause much breakage.

wpimath/src/main/native/include/frc/system/LinearSystem.h

@@ -22,6 +22,10 @@ namespace frc {
  *
  * For more on the underlying math, read
  * https://file.tavsys.net/control/controls-engineering-in-frc.pdf.
+ *
+ * @tparam States Number of states.
+ * @tparam Inputs Number of inputs.
+ * @tparam Outputs Number of outputs.
  */
 template <int States, int Inputs, int Outputs>
 class LinearSystem {