makefs: Add tests for the -T flag

Add tests for the -T flag to each makefs backend. This includes tests
for both mtree and directory scan options.

PR: 285630
Sponsored by: Klara, Inc.
Sponsored by: The FreeBSD Foundation
Reviewed by: markj, emaste, kevans, jlduran
Differential Revision: https://reviews.freebsd.org/D49492