Continuing the migration from java.io.File to java.nio.file.Path, StandardDocFileFactory.StandardDocFile should be converted to use Path internally, and maybe renamed to PathDocFile.

This will help IDEs and other tools that want to use nio filesystems for the underlying storage.

As the code stands, there is an assumption that the underlying file system used by javadoc is the standard (java.io.File) file system. That is a potential source of internal exceptions for anyone using an alternate file system through the DocumentationTool API