Support RDFa output in number field formatter

Problem/Motivation

Similarly to #2034975: Test RDFa output in email formatter and other fields, we need to verify whether the default placement of the RDFa markup on the field wrapper is sufficient for the number field, and we need to add tests.

Proposed resolution

Try the number field to see what markup is generated. Add a test.

Remaining tasks

User interface changes

none

API changes

none