PCTelescope: Added support to define setup via the communicator associated with a coarse DM
* The implementation is general and works with any DM type
* The coarse DM must reside on a sub-communicato

PCTelescope: Added support to define setup via the communicator associated with a coarse DM
* The implementation is general and works with any DM type
* The coarse DM must reside on a sub-communicator of the parent (fine) DM. This is checked during setup.
* Support for using coarse DMs requires the user compose methods for the field scatter between two topologically identical DMs defined on different communicators.
* Currently only works with KSPSetComputeOperators, although it is straightforward to add the extra hooks to support assembled operators

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