fileSize as double is limited

[MarcAntoine-Arnaud]

representing a fileSize as double is limited due to mantisse.
It may rounded values with giga bytes file as the mantisse cannot display decimals bytes.

Change it to nonNegativeInteger seams relevant, it just means it has to handle 64 bits (but it seems fine regarding that link: https://www.oreilly.com/library/view/xml-schema/0596002521/re86.html)

[JuergenGrupp]

Thank you, @MarcAntoine-Arnaud, I agree and support your proposed change.
I can apply this change, but prefer to do this after our current task (removing range) in a few weeks.