Address Todo items in AzimuthElevationToCartesianTransform

### Description

AzimuthElevationToCartesianTransform

* \todo Is there any real value in allowing the user to template
* over the scalar type? Perhaps it should always be double, unless
* there's a compatibility problem with the Point class.
*
* \todo Derive this class from TransformBase class.
* Currently, this class derives from AffineTransform, although
* it is not an affine transform.
*
* \todo Add a figure in the documentation that informs the formulas used in this class
* that are used to transform Cartesian to azimuth-elevation-radius

### Expected behavior

Noted todo items should be removed from code base.

### Actual behavior

### Versions

ITK version 5.0.0