Exchange halos with XIOS

[joewallwork]

Exchange halos with XIOS

Fixes #1067
Merges into halo-dynamics branch

Task List

• Linked an issue above that captures the requirements of this PR
• Defined the tests that specify a complete and functioning change
• Implemented the source code change that satisfies the tests
• Commented all code so that it can be understood without additional context
• No new warnings are generated or they are mentioned below
• The documentation has been updated (or an issue has been created to do so)
• Relevant labels (e.g., enhancement, bug) have been applied to this PR
• This change conforms to the conventions described in the README

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Change Description

This PR accounts for halo exchange when using XIOS for I/O.

I added a helper function getFieldLocalDoFs to get the number of DoFs for a given ModelArray::Type local to a rank (excluding halos).

Note that while the ModelArrays get halos, I don't tell XIOS anything about them, so we need to trim them off whenever we pass arrays to XIOS or receive them back.

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Test Description

Following the note above, the main changes to the tests are to do with how the values get set.

• Forcing test
• [/] Diagnostics tests
• Restarts tests

The diagnostics tests work fine for me locally so will need investigating, unfortunately.

Also, looking at the XIOS error for XiosReadWriteRestart_test.cpp (which I would've expected to work without changes) there seems to be a separate issue with CG, which will need investigating.

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Documentation Impact

TODO