Reverts "[wpimath] Constrain Rotation2d range to -pi to pi (#4611)"
This reverts commit d1d458db2b.
This broke multiple teams code in beta. It is also easier to limit the angle externally, then reconstruct a larger angle that got limited. This additionally adds comments to clarify the behavior and retains tests that were added in the reverted commit, and fixes a javadoc comment angle reference.
Comparison operators which compared against every class member variable
now use C++20's default comparison operators.
Also remove operator!= that in C++20 is now auto-generated from operator==.
