hmp: Rewrite strlist_from_comma_list() as hmp_split_at_comma()

Use g_strsplit() for the actual splitting.  Give external linkage, so
the next commit can move one of its users to another source file.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20230124121946.1139465-15-armbru@redhat.com>
2 files changed