Utilize latex preamble string parameters in image generation

[rbeezer]

An author's LaTeX macros may build on packages loaded through preamble customizations. So those packages need to be present so macros can be employed in image generation.

[rbeezer]

I was wrong about this. The latex-image-preamble element is meant to serve this purpose, and the string parameters are meant to serve an entirely different purpose. And, for good reason, there is not a way to migrate the values of these parameters through the mbx script and onto the relevant stylesheet.