add microdata support for file (core)

Should be resolved before RC.

This will not be possible unless some changes are made to core.

File is a reference-style field. The file theme function doesn't know anything about the field that it is being called from. It only knows about the file entity itself.

It was possible to enable microdata for image because there is a layer of indirection. A theme function that knows about the field settings calls the image theme function. This gives us a chance to pass the field's microdata settings to theme_image.

It was possible to enable microdata for taxonomy term because there is a settings page for the term. Therefore, the user could add the settings for the term to the entity itself and it would be loaded with the term.

Until we can change file_field_formatter_view() to account for microdata, this will not be possible.

No, discussions about how to integrate microdata into core haven't started yet and I don't plan to start them until there is more feedback about the API. I was leaving a note here for myself until that process happens.

It doesn't make sense yet for me to make issues against core. There is no chance that the changes needed will go into Drupal 7, and Drupal 8's rendering will be considerably different.