New composite poly mapper

The old approach used a fast path for a very narrow set of conditions and then used a slow path for everything else. This approach required two sets of code,

• GenericCompositePolydataMapper2
• CompositePolyDataMapper2

and had performance issues as the slow path was slower than OpenGL1 for some cases. This reworking consolidates the two approach together. The basic approach is that all blocks with the same VBO structure get grouped together and rendered as one. The number of different VBO structures is small so this results in a a small number of things to render.

Each of those things (handled with a Helper class) gets rendered using its own VBO and IBOs with special code to handle the cases where uniforms have to be changed between blocks etc.

The results are generally much faster. Some additional optimizations have resulted in further performance improvements. Generally this new class is as fast as the old fast path and tens to hundreds of times faster for the slow path.

This class is still complex and could probably be reworked another three times. The complexity is largly driven by how complex the task is as each block can have different primitives, point/cell data arrays, etc.

This topic adds four more tests for this class. As this class is the workhorse for ParaView it really needs far more testing in VTK. The four additional tests cover some use cases I know tend to cause issues.