RKDP is strictly better in terms of accuracy per unit of work. We used
RKF45 for sim physics in the 2021 season, but we transitioned to RKDP
before the 2022 season.
* Rename Butcher tableau sections in NumericalIntegration such that
top-left is c, top-right is A, and bottom-right is b
* Move edu.wpi.first.math.Discretization to
edu.wpi.first.math.system.Discretization
* Sort Java Discretization to match C++ function order
* Add tests for Java Discretization
* Required adding Runge-Kutta time-varying impl to tests
* Move C++ Runge-Kutta time-varying impl to tests only
* Users don't need it
Also refactored RKF45 implementation to match the new style, which is
easier to read.
The tests were switched from RKF45 to RKDP since it's more accurate.
