MFC 250223:

MFC 250223:
Similar to 233760 and 236717, export some more useful info about the
kernel-based POSIX semaphore descriptors to userland via procstat(1) and
fstat(1):
- Change sem file descriptors to track the pathname they are associated
  with and add a ksem_info() method to copy the path out to a
  caller-supplied buffer.
- Use ksem_info() to export the path of a semaphore via struct kinfo_file.
- Teach fstat about semaphores and to display their path, mode, and value.

git-svn-id: svn://svn.freebsd.org/base/stable/8@252164 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f