We have found several times now when writing code using Cogl that it
would really help if Cogl's matrix stack api was public as a utility
api. In Rig for example we want to avoid redundant arithmetic when
deriving the matrices of entities used to render and we aren't able
to simply use the framebuffer's matrix stack to achieve this. Also when
implementing cairo-cogl we found that it would be really useful if we
could have a matrix stack utility api.
(cherry picked from commit d17a01fd935d88fab96fe6cc0b906c84026c0067)