truncate(1): Add hole-punching support

This commit adds hole-punching support to the truncate(1) utility. If
the option -d is specified, truncate(1) performs zeroing, and if
possible hole-punching in case the operation is supported by the
underlying file system of the specified files.

Sponsored by: The FreeBSD Foundation
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D31556