`GetContentFieldsW`: pass directory name

[johnd0e]

Description of the new feature or improvement

Use cases:

1. Sometimes data should be prepared once for all the files in the directory, so better to do it in GetContentFieldsW than in GetContentDataW
2. Some ContentColumns may have meaning only in particular directory, so it would be nice to determinate it at once, and not to call GetContentDataW for every file.

Proposed technical implementation details (optional)

No response

[johnd0e]

@shmuz @zg0