Use same string encoding for results from all fileserver backends.
Use same string encoding for results from all fileserver backends.

Each fileserver backend might return files using a different encoding
which will lead to a backtrace when the resulting file set is sorted().

This fixes #20499 and applies the same security measure to other
fileserver functions where appropriate.

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt