Local index addition for block distributed sparse domains

[e-kayrakli]

Addresses #12673 by adding addOn argument to the bulkAdd interface.

In order to track the local domain object, this PR also adds myLocDom to SparseBlockDom class similar to myLocArr.

While implementing this, I noticed the problem with the nnz field for SparseBlock. See #13410. I think that issue must be resolved before this PR is merged. The issue is somewhat subtle and hard to bump into. However, local index addition implemented in this PR will mess up nnz and probably none of the locales will be able to read the correct size of the domain.

TODO:

• Added test passes with CHPL_COMM=gasnet
• test/users/engin/sparse_bulk* passes
• Full paratest (local and gasnet)
• Doc
• Check if reasonable errors are generated when indices are OOB

[e-kayrakli]

@benharsh -- do you mind giving this a look?

[benharsh]

This generally looks fine to me. I'd prefer that we have a better default value for locales than nil, but that's OK for now.

[e-kayrakli]

Created #13526 to capture the special locale value idea.

Running some more tests to make sure I haven't missed anything. Thanks @benharsh

[e-kayrakli]

The word "nil" for the default argument value is dropped in docs for some reason, filed an issue: #13531