Blender Git Loki

Cleanup: Paint Cursor Refactor

The paint_draw_cursor function was handling the cursor drawing for 2D
and 3D views of all paint modes, calculating the brush radius, updating
the SculptSession data and updating and drawing all sculpt cursor
overlays for different tools. It was almost impossible to understand when
and what was being drawn and in which state the GPU matrix was.

Now everyting is organized into different functions, with clear
separation between modes, sculpt tool overlays and different drawing
setups. Update and drawing functions are also separated (this allows to
skip one PBVH query on each cursor drawing).

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8206