Deprecate file:filename since it is redundant with the name property of the content complex type.
Therefore we should at least:
- Make sure we always set the content/name sub-field when setting the file:content or files:files/*/file property of a document. This means that the filename field of the input Blob must not be null.
- Have some migration code / procedure to set content/name if not set, using the file:filename field assuming it is set.
- Make sure we always use content/name when reading / displaying a blob's filename.