Distributed GridapEmbedded and AgFEM

[pmartorell]

@fverdugo ,

this is a distributed extension of GridapEmbedded that includes the parallelization of the AgFEM. See 10.1016/j.cma.2019.112583.

The distributed aggregation has the following interface. Note that the bgmodel may be updated during the aggregation process to accommodate remote aggregation roots in the ghost layer.

bgmodel,cutgeo,aggregates = aggregate(strategy,cutgeo)

There is a significant simplification of the graph generation in contrast to 10.1016/j.cma.2019.112583. Here we leverage the PartitionedArrays.jl machinery to update the graph communicators.

Also, note that in GridapEmbedded we may have empty subdomains which are not currently supported in Gridap and GridapDistributed.

FYI: @santiagobadia @ericneiva