Clarify Stroke and Fill Icons

[fuguesoft]

It's not immediately obvious to me which circle here represents the fill/stroke of an object:

I think changing the shapes might dispel any initial confusion.
Affinity, for example, uses two different shapes to distinguish between the stroke and fill control:

[Keavon]

These currently have no relation to stroke and fill. They are primary and secondary colors. The tools can pick from either, or a custom, on a tool-by-tool basis in the control bar. It is that fact which is not presently well-designed and is one of the higher priority redesign tasks that will be covered in those listed within #3646. Since that already tracks it, to avoid semi-pertinent duplicates, I'll close this (but feel free to still discuss here if you want to add more details).