SoA: Public Getter for Names

[ax3l]

Summary

Expose the names to public member functions.

Additional background

Needed for Python bindings. Follow-up to #4163

Checklist

The proposed changes:

• fix a bug or incorrect behavior in AMReX
• add new capabilities to AMReX
• changes answers in the test suite to more than roundoff level
• are likely to significantly affect the results of downstream AMReX users
• include documentation in the code and/or rst files, if appropriate

[ax3l]

Let me know what you prefer.

In fact in Python bindings I prefer the alternative of returning an empty list over having to handle an exception.