UsePath instead of File in the API

[laeubi]

To encourage user to use modern API all File references should be replaced by Path references, even though currently due to the Plexus-Scanner-API only File pathes are actually supported.

[laeubi]

Seems a prerequisite here:

• Move to Path API (and increase major version to 4) plexus-utils#224

[laeubi]

Another option would be to get rid of the Scanner API completely and return a DirectoryStream instead ...

[laeubi]

I have checked m2e and it uses AbstractScanner only (so directory scanner is not really a concern for it and mostly used for the default impl) and mostly uses it to check if a delta found matches.

@kwin as you recently made some plugins Build API aware, I wonder if you can shade some light how useful the methods newScanner/newDeleteScanner are actually are, I feel like we can simply get rid of them completely and just offer a newDeltaStream() that list all items (deleted, new, changed) and then users can use other method of the context to decide what state they actually have (if the implementation itself actually is not using a different filtering mechanism already) ...