Generator always fails to find config file on Windows

### Description

This is due to the code in PluginUtils.swift which uses $0.path.lastComponent to get the filename of files in a FileList (which is SwiftPM package plugin API).

Unfortunately, path.lastComponent is broken on Windows, but there is a functional replacement url.lastComponent in manifest versions 6.0 or later.

When can swift-openapi-generator adopt 6.0 manifest version, or what can we do to resolve this on Windows?

Start with PluginUtils.swift and the FileList path handling described in the issue, then check the available SwiftPM manifest version and plugin API on Windows. Done means the generator reliably finds configuration filenames on Windows, either through the supported URL property or an approved manifest-version change.

Written by the indexing model from the issue text.