Issue Description:

Say I have a folder with one or more periods in its name, such as foo.bar. Currently, SPM sees this as a a .bar bundle and forces me to either list it as a resource, or to exclude it from my target.

Is there any way to make SPM "leave it alone" and just treat it as a regular old directory? I want the files within it to be treated as normal. E.g. asset catalogs are picked up as resources, .swift files are picked up as sources, etc.

For background:

• On macOS, a folder with a directory in its name will be treated as a bundle only if there's a registered UTI that conforms to com.apple.bundle which is associated with that filename extension. Even still, bundles are really just directories, and you can still browse their contents.

• On Linux, dots in folder names have no special significance, and there is no "bundle" concept, at all!

Forum thread: https://forums.swift.org/t/supporting-folders-with-dots-in-their-names/50251