Custom intrinsic scopes

[eleon]

We currently have predefined intrinsic scopes such as QV_SCOPE_USER and QV_SCOPE_PROCESS. It would be helpful to allow users to define intrinsic scopes that external libraries can use for computing.

Let's say I have an application that calls into a QV-enabled MPI library and this application wants the MPI library to use specific cores for doing MPI progress. Since the app cannot change the MPI API, passing these resources as a scope has to be done implicitly. The app could create an intrinsic scope via:

## Mirror call of qv_scope_get
qv_scope_put(qv_context_t *ctx, qv_scope_t **scope, char *name);
## For example 
qv_scope_put(ctx, bottom_hw_threads_scope, 'QV_SCOPE_UTILITY'); 

The MPI library would then use the resources associated with QV_SCOPE_UTILITY to launch its progress threads:

qv_scope_get(ctx, QV_SCOPE_UTILITY, &progress_th_scope); 

Among other things, this may involve changing the type of iscope in

qv_scope_get(qv_context_t *ctx, qv_scope_intrinsic_t iscope, qv_scope_t **scope)

Alternatively, we can allow users to custom-define a specific intrinsic scope, say QV_SCOPE_UTILITY, rather than allow them to create custom intrinsic scopes in general. This would work too and, perhaps, would make the implementation easier 😃

In this case the following call would work, but it would only be supported for QV_SCOPE_UTILITY (and other specific names if we decide to extend this capability):

qv_scope_put(ctx, bottom_hw_threads_scope, QV_SCOPE_UTILITY); 

Note that QV_SCOPE_UTILITY would be an enum, not a string, since QV would control the names of all the intrinsic scopes 😄