Allow users to see a preview of what FileImporter was able to extract from the wikitext configuration files, possibly in a JSON format.

Technically: Provide an API or special page to dump the contents of a successfully parsed WikiTextConversions object.

This is relevant for two reasons:

• A lot of minor mistakes that can happen in the configuration files can not be detected early on, only when a file transfer runs into an actual issue. A typical example is a missing +. This is not a technical error that can be detected by a tool, but it might be a logical error. Providing the parse result in a human-readable format (JSON mostly is human-readable) allows users to see such mistakes before a bad import is made.
• We might want to switch from configuration files formatted as wikitext to JSON. The proposed API or special page would effectively provide a semi-automatic conversion feature.