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'

Fix T80475, bad bevel: side vertex in bad plane in some cases.

Needed a better normal to for plane to offset into when there are
non in-plane edges between two beveled edges. It was using the vertex
normal, which is just wrong.

Differential Revision: https://developer.blender.org/D9508

Fix T81651, exact boolean modifier incorrect if operand hidden.

The code was trying to ignore hidden geometry when doing boolean,
which is correct when used as a tool, but not when a modifier.
Added a "keep_hidden" argument to bmesh_boolean to distinguish the
two cases.
Also fixed a bug when the tool is used with hidden geometry that
is attached to unhidden geometry that is deleted by the operation.

Fix T81651, exact boolean modifier incorrect if operand hidden.

The code was trying to ignore hidden geometry when doing boolean,
which is correct when used as a tool, but not when a modifier.
Added a "keep_hidden" argument to bmesh_boolean to distinguish the
two cases.
Also fixed a bug when the tool is used with hidden geometry that
is attached to unhidden geometry that is deleted by the operation.