We had %VALUE_STRSPLIT_MODE_MULTILIST_WITH_ESCAPE, which was used
by "match.interface-names". This uses nm_utils_strsplit_set_full()
with %NM_UTILS_STRSPLIT_SET_FLAGS_ALLOW_ESCAPING and
_nm_utils_unescape_plain().

We want eventually to use nm_utils_escaped_tokens_split() everywhere.

We already have %VALUE_STRSPLIT_MODE_ESCAPED_TOKENS, which splits the
list at ',' (and strips whitespaces at the around the delimiter). That
differs from what %VALUE_STRSPLIT_MODE_MULTILIST_WITH_ESCAPE did, which
also considered whitespace a delimiter.

So, we need a new mode %VALUE_STRSPLIT_MODE_ESCAPED_TOKENS_WITH_SPACES
which replaces the previous mode.

Note that the previous implementation did almost the same thing. In
fact, I cannot imagine examples where they behaved differently, but
my feeling is that there might be some edge cases where this changes
behavior.