Cleanups to Resolver/UnboundTemplate details

[jhawthorn]

This PR includes cleanup of parsed details handling the towards a redo of #39362, which I never completed.

• Introduces a Struct to store the parsed details instead of using a hash (as suggested in Use PathParser for finding templates too  #39362).
• Parses and stores the full set of details on UnboundTemplate instead of treating it as just an options hash to pass to Template. This will allow filtering later.
• Determines virtual_path from the filesystem instead of from the requested path

[kaspth]

Cool! Feels a little odd how often we're passing all the details around instead of generally extracting a Template::Details object, but that could be later, or it doesn't make sense etc.

[jhawthorn]

Feels a little odd how often we're passing all the details around instead of generally extracting a Template::Details object, but that could be later, or it doesn't make sense etc.

I agree it's a bit odd. Complicating it is that we have details in many forms: parsed from a filename, the details requested by the user (arrays for each key), a plain Object representing the requested details, and finally the handler class used by Template. I think a class (or pair of classes for requested vs found) would make sense for that, but I'd like to see what refactoring shakes out first.