Blender Git Loki

Fix texture paint UV dilation algorithm

Two aspects are addressed:

- Correct computation of dilation distance,
so that dilated boundaries remain parallel to the original boundaries
(and with the actual distance specified as bleed distance).

- Dilate with regard to adjacent seams
instead of adjacent triangle edges, for a more correct result.
This is especially important in the case of concave shapes,
where spikes could overlap with actual geometry.

See: D4436