Blender Git Loki

Fix wireframe overlay not blending over paint overlay correctly

When using wireframe opacity, the paint overlay needs to be drawn
before the wireframes in order to alpha blend correctly.
Sculpt overlays were also affected by this, so this commit refactors
this part of the code in case other overlays needs to be added in
the future.

Reviewed By: Mets

Differential Revision: https://developer.blender.org/D12235