[WIP] Refactor to use package extensions and render all vector types

[asinghvi17]

• Explicit interface to render SVG, PDF, and EPS. Sufficiently general that we can potentially extend this in future to render any vector format using ImageMagick.
• Package Extensions on scatter so we can use that directly with cached types
• Move CairoMakie rendering code to an extension
• Refactor rendering code a bit