More validation of entity property names

[matthew-white]

We need to do a little more validation of entity property names. pyxform also does that validation, so this issue is for after v2022.3.

What we do today:

• A property cannot be named name or label.

(Not yet implemented:) We should also require that property names:

• Be valid XML identifiers (start with letter or _, can only include letters, numbers, -, _, .)
• Not start with __

This is similar to (the same as?) some of the validation that we do today for dataset names.

Notes for the QA team

pyxform has already been doing this validation for XLSForms. Now we are also doing this validation for XML XForms. It'd be good to verify that this validation happens when an XML XForm is uploaded.

[lognaturel]

This is similar to (the same as?)

Yes, but it's ok for property names to include periods (part of valid XML identifiers) but not dataset names (so it's easier to have .csv, .zip, etc exports)

[srujner]

Tested with Success!

[dbemke]

Tested with Success!