Blender Git Loki

Fix T62240: Bleed artifacts with degenerate triangles

This makes degenerate triangles be ignored, as they cause artifacts and
don't contribute to the result anyway. There is an extra cost for
all triangles, to check if they are degenerate. Though not ideal, this
seems to be the safest solution at the moment (see code comments).

This commit also changes the clamp value for the bleed len_fact from 5
to 10, to give good corner results with some sharper angles, considering
they will be rounded later.

A lot of the texture paint initialization code could be optimized
by caching the results throughout the session, instead of rerunning it
for each stroke. Stroke initialization is way too expensive at the
moment, and does many redundant computations.