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