The knife code currently calls the `BLI_bvhtree_overlap` function that
tests the overlap between the mesh tree and an AABB that encompasses the
points projected in the clip_start, clip_end and or clip_planes of the
view.
This resulted in many false positives since the AABB is very large.
Often all the triangles "overlapped".
The solution was to create a new function that actually tests the
intersection of AABB with a plane.
Even not considering the clip_planes of the view, this solution is more
appropriate than using overlap.
Differential Revision: https://developer.blender.org/D8229
20558848d3