Blender Git Loki

Cloth: completely exclude fully pinned triangles from collision.

Currently such triangles are effectively already excluded, because
the calculated forces are not applied to pinned vertices. However
these forces are still being computed, which is inefficient.

This adds an early check for triangles where all vertices are
pinned during BVH overlap detection, which significantly speeds
up certain use cases with big fully pinned areas that happen to
overlap a collider. In case of self collision both triangles must
be fully pinned to exclude safely, because the computation is
symmetric and handles two triangles at the same time.

Differential Revision: https://developer.blender.org/D10041