[geometry] Method to make a DOMPoint homogeneous

[zcorpan]

https://drafts.fxtf.org/geometry/#DOMPoint

https://en.wikipedia.org/wiki/Transformation_matrix#Perspective_projection

Since the result of matrixTransform() can be a non-homogeneous point (w != 1), it might be useful with a method that makes the point homogeneous (if possible).

Thoughts? @fsoder @smfr @hwanseung

[fuchsia]

I don't think they stop being homogenous coordinates when w departs from unity. But you can do "perspective division" which divides each component by w, and returns w to one under most situations.