Refactored continuous distributions to v4 (AsymmetricLaplace, HalfStudentT, ExGaussian, Interpolated) (#4746)

* Refactored continuous distributions to v4 (AsymmetricLaplace, HalfStudentT, ExGaussian, Interpolated)

* Refactored tests for new distributions

* Added RV size testing for Interpolated

* Convert arguments in Interpolated to constant and add comments

Co-authored-by: Ricardo <ricardo.vieira1994@gmail.com>

Author: kc611