MUMPS: Various improvements to the package (#22575)
MUMPS: Various improvements to the package (#22575)

Use `conflicts` directive whenever possible.
This allows failing early when conflicting variants are used.

Do not silently ignore `+parmetis` variant when `~metis`.
Instead throw an error during concretization.

Simplify the "Makefile.inc" generation.
This will make easier to add new variants in the future.
LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack