Stop generating project headers that shadow SwiftPM public headers

Projects that pull in SwiftPM C directory-targets with wrapper-style public headers, like nanopb, no longer risk Multiple commands produce... failures when copying framework headers, nor #include nested too deeply errors when consumers include their module-qualified headers. Tuist now tracks both the headers selected as framework public headers and the public-directory headers shadowed by that selection, and excludes the shadowed duplicates from the generated project header glob in addition to de-duplicating framework copy destinations.