error messages: condition chaining (#40173)

Create chains of causation for error messages.

The current implementation is only completed for some of the many errors presented by the concretizer. The rest will need to be filled out over time, but this demonstrates the capability.

The basic idea is to associate conditions in the solver with one another in causal relationships, and to associate errors with the proximate causes of their facts in the condition graph. Then we can construct causal trees to explain errors, which will hopefully present users with useful information to avoid the error or report issues.

Technically, this is implemented as a secondary solve. The concretizer computes the optimal model, and if the optimal model contains an error, then a secondary solve computes causation information about the error(s) in the concretizer output.

Examples:

$ spack solve hdf5 ^cmake@3.0.1
==> Error: concretization failed for the following reasons:

   1. Cannot satisfy 'cmake@3.0.1'
   2. Cannot satisfy 'cmake@3.0.1'
        required because hdf5 ^cmake@3.0.1 requested from CLI 
   3. Cannot satisfy 'cmake@3.18:' and 'cmake@3.0.1
        required because hdf5 ^cmake@3.0.1 requested from CLI 
        required because hdf5 depends on cmake@3.18: when @1.13: 
          required because hdf5 ^cmake@3.0.1 requested from CLI 
   4. Cannot satisfy 'cmake@3.12:' and 'cmake@3.0.1
        required because hdf5 depends on cmake@3.12: 
          required because hdf5 ^cmake@3.0.1 requested from CLI 
        required because hdf5 ^cmake@3.0.1 requested from CLI

$ spack spec cmake ^curl~ldap   # <-- with curl configured non-buildable and an external with `+ldap`
==> Error: concretization failed for the following reasons:

   1. Attempted to use external for 'curl' which does not satisfy any configured external spec
   2. Attempted to build package curl which is not buildable and does not have a satisfying external
        attr('variant_value', 'curl', 'ldap', 'True') is an external constraint for curl which was not satisfied
   3. Attempted to build package curl which is not buildable and does not have a satisfying external
        attr('variant_value', 'curl', 'gssapi', 'True') is an external constraint for curl which was not satisfied
   4. Attempted to build package curl which is not buildable and does not have a satisfying external
        'curl+ldap' is an external constraint for curl which was not satisfied
        'curl~ldap' required
        required because cmake ^curl~ldap requested from CLI 

$ spack solve yambo+mpi ^hdf5~mpi
==> Error: concretization failed for the following reasons:

   1. 'hdf5' required multiple values for single-valued variant 'mpi'
   2. 'hdf5' required multiple values for single-valued variant 'mpi'
    Requested '~mpi' and '+mpi'
        required because yambo depends on hdf5+mpi when +mpi 
          required because yambo+mpi ^hdf5~mpi requested from CLI 
        required because yambo+mpi ^hdf5~mpi requested from CLI 
   3. 'hdf5' required multiple values for single-valued variant 'mpi'
    Requested '~mpi' and '+mpi'
        required because netcdf-c depends on hdf5+mpi when +mpi 
          required because netcdf-fortran depends on netcdf-c 
            required because yambo depends on netcdf-fortran 
              required because yambo+mpi ^hdf5~mpi requested from CLI 
          required because netcdf-fortran depends on netcdf-c@4.7.4: when @4.5.3: 
            required because yambo depends on netcdf-fortran 
              required because yambo+mpi ^hdf5~mpi requested from CLI 
          required because yambo depends on netcdf-c 
            required because yambo+mpi ^hdf5~mpi requested from CLI 
          required because yambo depends on netcdf-c+mpi when +mpi 
            required because yambo+mpi ^hdf5~mpi requested from CLI 
        required because yambo+mpi ^hdf5~mpi requested from CLI 

Future work:

In addition to fleshing out the causes of other errors, I would like to find a way to associate different components of the error messages with different causes. In this example it's pretty easy to infer which part is which, but I'm not confident that will always be the case. 

See the previous PR #34500 for discussion of how the condition chains are incomplete. In the future, we may need custom logic for individual attributes to associate some important choice rules with conditions such that clingo choices or other derivations can be part of the explanation.

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Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

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