fileapi: does not expose INTERFACE libraries
The fileapi feature, initially tracked by #18398 (closed), does not include INTERFACE libraries in the codemodel output as the server mode does. It is a bug that the server mode exposes them.
This is because interface libraries are not included in the generated build system. They cannot hold custom commands or any other build rule. There is no "make" or "ninja" build target for them. They do not appear in the VS or Xcode generator projects.
In order to fix this, we need to make interface libraries first-class members of the generated build system. Once that is done then the fileapi can expose them because the proper structures will be available internally.