RFE: do not allow dangling symlinks

[smoser]

Generally speaking, installed packages should not have dangling symlinks. There are definitely cases where a symlink is resolved across a package/subpackage/dependency-package border, so those might need to be accounted for.

I think I would like melange to fail if a package contains dangling symlinks that are not resolved within the current package or any of subpackages. (for example, python-3.12 links to python3 which is provided by python-3.12-base).

We would want to allow for this to be disabled for cases where a package symlinked to a package provided by a dependency.