MueLu: Coloring algorithms support

[GrahamBenHarper]

As noted in some performance results from #12351, it seems like most of the aggregation coloring algorithms we support are really slow on GPU. I've never opted to use some of them personally, so I don't know what they're good for and if they're worth supporting. The purpose of this discussion is to simply recall if there are cases where these coloring algorithms are useful, what the purposes are, and if we should continue supporting them all.

As a reminder, here are the aggregation algorithms we have according to source (serial and default are the same here):

[gbharpe@vortex66 src]$ grep -rn aggAlgo
Graph/UncoupledAggregation/MueLu_UncoupledAggregationFactory_kokkos_def.hpp:241:    std::string aggAlgo = pL.get<std::string>("aggregation: coloring algorithm");
Graph/UncoupledAggregation/MueLu_UncoupledAggregationFactory_kokkos_def.hpp:242:    if(aggAlgo == "mis2 coarsening" || aggAlgo == "mis2 aggregation")
Graph/UncoupledAggregation/MueLu_UncoupledAggregationFactory_kokkos_def.hpp:256:      if(aggAlgo == "mis2 coarsening")
Graph/UncoupledAggregation/MueLu_UncoupledAggregationFactory_kokkos_def.hpp:261:      else if(aggAlgo == "mis2 aggregation")
Graph/UncoupledAggregation/MueLu_UncoupledAggregationFactory_kokkos_def.hpp:318:        } else if(aggAlgo == "serial") {
Graph/UncoupledAggregation/MueLu_UncoupledAggregationFactory_kokkos_def.hpp:321:        } else if(aggAlgo == "default") {
Graph/UncoupledAggregation/MueLu_UncoupledAggregationFactory_kokkos_def.hpp:324:        } else if(aggAlgo == "vertex based") {
Graph/UncoupledAggregation/MueLu_UncoupledAggregationFactory_kokkos_def.hpp:327:        } else if(aggAlgo == "vertex based bit set") {
Graph/UncoupledAggregation/MueLu_UncoupledAggregationFactory_kokkos_def.hpp:330:        } else if(aggAlgo == "edge filtering") {
Graph/UncoupledAggregation/MueLu_UncoupledAggregationFactory_kokkos_def.hpp:333:        } else if(aggAlgo == "net based bit set") {

I should also remark the MueLu user's guide is out of sync with our actual coloring support. See Table 5.6 on page 36. "Vertex based" and "edge filtering" are not documented, and it isn't clear what they're useful for or how they work.