Use file-name-quote{,d-p} in files-tests.el

Use file-name-quote{,d-p} in files-tests.el

* test/lisp/files-tests.el
(files-tests-file-name-non-special-quote-unquote): New test.
(files-tests--file-name-non-special--subprocess): Simplify.
(files-tests--file-name-non-special--buffers)
(files-tests--with-temp-non-special)
(files-tests-file-name-non-special-directory-file-name)
(files-tests-file-name-non-special-file-in-directory-p)
(files-tests-file-name-non-special-file-name-all-completions)
(files-tests-file-name-non-special-file-name-as-directory)
(files-tests-file-name-non-special-file-name-completion)
(files-tests-file-name-non-special-file-name-directory)
(files-tests-file-name-non-special-find-backup-file-name)
(files-tests-file-name-non-special-make-nearby-temp-file):
Use `file-name-quote' and `file-name-quoted-p', respectively.