support for only single patch between processors (e.g. ProcessorTopology::procPatchMap())

Functionality to add/problem to solve

Some functionality only supports a single processor patch. Sometimes there can be more than one patch between processors. E.g. processorCyclic (processor patch with cyclic transformations), overset (introduces additional lduInterfaces to handle the interpolation)

See e.g.

ProcessorTopology::procPatchMap()

which is used to lookup a patch given a remote processor (used in snappyHexMesh/extrudeMesh)