Adding CSV I/O to the pointdatatofld module in FieldConvert

Issue/feature addressed

Although the documentation says that it is possible to use the pointdatatofld module in FieldConvert with .csv files, this was not possible. This MR fixes this issue by adding the option to read a .csv file too.

Proposed solution

Check the file extension of the option frompts in ProcessPointDataToFld.cpp and read the data based on the extension.

Implementation

The fix is small and self explanatory.

Tests

One new test called "pointdatatofld_csv_input" has been added. This test compares the field obtained with the pointdatatofld module with a reference field specified in the file flat-plane.fld.

Suggested reviewers

@jisler @margarida.moragues

Notes

Please add any other information that could be useful for reviewers.

Checklist

• [ ] Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).