Add a file size field to the REST API and use its value when fetching media

[johnbillion]

This is a follow-up to #6.

The file size is not exposed by default in the WordPress REST API media endpoint. This plugin should add a new field to the REST API which exposes it, and then reads that value in Factory::create() and sets the file size via $item->set_file_size() if the field exists.

This would solve the problem of not having file size information when this plugin is used for sharing media within a Multisite network.

Longer term, we should open a ticket for WordPress core to get the file size added to the REST API too.

[tfrommen]

Just noting that, for audio files, this information is already present in $data->media_details->filesize. For any other media type, it is not.

[tfrommen]

Also, I just created https://core.trac.wordpress.org/ticket/52840.

[roborourke]

Older issue I know but any change to enable this would have to be in code running on the source site, this plugin won't necessarily be enabled there.