Adjust angle threshold defaults to dissolve verts as before,
while preserving selected geometry.
The new behavior works as follows:
- If a dissolve terminates on an edge loop or the the corner vert of a
face, do the dissolve.
- If a set of dissolve edges (either a chain, or a set of 3+ edges)
crosses a loop cut, do the dissolve.
- If a chain of dissolve edges touch the corner of an unselected face,
and then leave in a different direction without crossing a loop cut,
preserve that vert. Just because the selection touches it doesn't mean
it should be altered.
- If a dissolve edge is separating two triangles,
then the face join creates a quad. Users generally prefer
and strive to create meshes that contain quads.
Instead of destructively dissolving the corners of the quad and
automatically turning it to a triangle or wire,
instead prefer to preserve the quad.
Ref !141097