Speed up finding patch components in new boolean.

By checking if a cell has already been processed in the finding patch
component code, an enormous speedup happens. This only will be
noticeable if there are lots of patches, and some cells with a
large number of patches.

Speedups for finding cells in new boolean.

In case where there are coplanar instersections where
each part has a lot of triangles, the finding-cells algorithm was
very inefficient. This uses a Set instead of a Vector to keep track
of a cell's patches, avoids going through all patch x patch combinations,
avoids going through all patches to renumber after a merge, and
merges smaller patch-sixe cells into larger ones.
All this reduces the time to find cells in the cited case by a factor of 10.

Add performance timing to mesh_boolean.cc.

You can uncomment the PERFDEBUG define to get timings.

Speedups for new boolean. Better hash function for verts.

The existing hash function didn't work well with Set's method of
masking to the lower bits, because many verts have zeros in the
lower bits.
Also, replaced VectorSet with Set for Vert deduping.

Previous commit forgot to guard some things with #ifdef WITH_GMP.

Improve speed of Constrained Delaunay Triangulation with exact arith.

By using floating point filters, the speed improves by a factor of 2 to 10.
This will help speed up some cases of the Exact Boolean modifier.
Changed the interface of mpq2::isect_seg_seg to not return mu, as it was
not needed and not calculating it saved 15% time.

Fix exact boolean coplanar problem due to inexact transform.

This is an addendum to previous boolean fix, where the object
transformation was "cleaned". Now the operand one is too.
This fixes the issue shown in the video in T82301 when you move
a column around the XY plane with the top and bottom faces
supposedly coplanar with a cube. The transformation matrix when
you do that has a tiny offset in the z component.

Merge branch 'blender-v2.91-release'
Bring in exact boolean fix.

Fix T82736, Exact Boolean fail with repeated subtraction of same object.

Two problems were fixed. One, the code for dissolving vertices
left a face around if dissolving a vertex would leave less than
three vertices. Instead, the face should be deleted.
Two, with transformations like "rotate 180 degrees", this should
be no problem with exact, but the current transformation matrix
has very small non-zero entries where it shouldn't. Cleaning the
transformation matrix makes it more likely that user expectations
about coplanar faces will be fulfilled.

Merge branch 'blender-v2.91-release'