Polygon clipping support in ClipField and EquiZ MIR.

[BradWhitlock]

I tried EquiZAlgorithm on a mesh with octagons and found that it could not handle polygons (just tri/quad).

This PR:

• Added a TopologyMapper test that intersects 2 meshes with octagons and runs EquiZ on the resulting matset.
• Enhanced ClipField and EquiZAlgorithm to handle polygons with 5-8 sides.
• Added polygonal clipping tables for polygons with 4-8 sides. The clipped shapes are kept in larger polygons rather than splitting to quad/tri. This makes fewer zone fragments (also looks better and could be a little faster).
• Fixes a glitch in the "originalElements" field when we remove degenerate zone fragments.
• The line count looks large here but it is mostly look up tables.

Here we see VisIt and Axom. VisIt looks wrong for quad shapes here and successive refinement into quad/tri causes more irregular edges (also not showing all mesh edges it makes). Axom keeps zone fragments together as polygons through clipping so fewer fragments and edges are needed.

Here is another example of how clipping polygons results in fewer zone fragments: