Add missing getters for `mediaInline`

[Chris Fuller]

It doesn’t have a getter for its mediaType() or alt(). This is just an accidental oversight and needs to be fixed.

While I’m at it, I’m also adding a marker interface shared by Media.FileOrLinkMedia and InlineMedia that declare getters and setters for id, collection, and occurrenceKey. This will be helpful for Jira, which needs to be able to find all internal media nodes to reconcile them with issue attachment data.

[Chris Fuller]

Fixed in 0.27.0, with a critical bugfix (InternalMediaNode needs to extend Node to be usable) in 0.27.1.