The code to detect non-trivial coplanar intersection sometimes
falsely said there wasn't one. This caused some coplanar intersections
to be missed. Also added a test for this case.
Instead of calculating exact normals for all faces, just do it
for those that potentially intersect. A big improvement for dense
meshes that only intersect in relatively few places.
The code that found coplanar clusters was not updating a bounding box.
Also, code that was detecting non-trivial coplanar intersects was
slightly wrong, but that would not have caused any functional problems.
This is for design task T67744, Boolean Redesign.
It adds a choice of solver to the Boolean modifier and the
Intersect (Boolean) and Intersect (Knife) tools.
The 'Fast' choice is the current Bmesh boolean.
The new 'Exact' choice is a more advanced algorithm that supports
overlapping geometry and uses more robust calculations, but is
slower than the Fast choice.
The default with this commit is set to 'Exact'. We can decide before
the 2.91 release whether or not this is the right choice, but this
choice now will get us more testing and feedback on the new code.
