Previously, the content metadata displayed next to a topic's content
type (like "Article: 1800 words") was fairly generic and could result in
strange data being displayed if a scraper fetched it for an
inappropriate type (for example, displaying word count for videos).
This creates an enum to hold all the different content metadata fields,
and moves some logic into that class to handle deciding which fields to
show for different types, and the formatting logic for values.
Deimos
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