Replaces mpp_recv and mpp_send and uses mpi_gather and mpi_scatterv within mpp_scatter_pelist

[ganganoaa]

Description
The original mpp_scatter used point-to-point communications: _mpp_recv and mpp_send to gather at and scatter from the root pe. This update replaces the point-to-point communications and uses standard collective communications: mpi_gather and mpi_scatterv to achieve the data transfer.

Fixes # (issue)

How Has This Been Tested?
Tested locally with Intel oneAPI (v2023.1.0); intel ifort (v2021.9.0).

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes

[bensonr]

@ganganoaa - can you include this new version in parallel with the existing version? This will allow us evaluate performance in many different scenarios via different test cases.

[ganganoaa]

It has issues with non-MPI compilation. So, I am updating it.