Data attribute properties are not very consistent in diff view

I introduced in XWIKI-19044 some data-property-name attributes in the macro for displaying diff in order to be able to retrieve consistent data without needing to rely on the translations text.
Now I haven't been entirely consistent in the values set there: for example in case of the content property of a page the value is content, for the content property of an xobject it's also content but for the content of an attachment it's attachment.content.