XIOS: allow reading and writing in the same run

[joewallwork]

XIOS: allow reading and writing in the same run

Fixes #1007
Merges into #1011

Task List

• Defined the tests that specify a complete and functioning change (It may help to create a design specification & test specification)
• Implemented the source code change that satisfies the tests
• Documented the feature by providing worked example
• Updated the README or other documentation
• Completed the pre-Request checklist below

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Change Description

In order to allow the reading and writing of a field in the same run, it turned out that I needed to create an additional field for the reading and to associate the two together with a field reference. They point to the same data but it allows the field for reading to have different I/O properties, e.g., "instant", "averaging", "once". It does not appear to be required to create an additional field for writing - you can just use the 'base' field.

To facilitate the creation of the inherited field, this PR adds a createInheritedField member function. Helper functions getFileIOType and setFieldOperation are also introduced.

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Test Description

To demonstrate that the functionality does indeed work, I've introduced an additional test XiosReadWriteRestarts_test. It reads the xios_test_input.nc file in as a restart in ModelState format, writes it back out as a restart dump, and then checks the corresponding files exist.

I also removed XiosField_test as it's no longer needed.

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Documentation Impact

A developer note has been added in the XIOS doc page.

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Pre-Request Checklist

• The requirements of this pull request are fully captured in an issue or design specification and are linked and summarised in the description of this PR
• No new warnings are generated
• The documentation has been updated (or an issue has been created to track the corresponding change)
• Methods and Tests are commented such that they can be understood without having to obtain additional context
• This PR/Issue is labelled as a bug/feature/enhancement/breaking change
• This change conforms to the conventions described in the README

[joewallwork]

How bizarre. The tests all pass on my machine (even after removing the build directory and rebuilding). I'll debug this next week.