refactor(preg): report unmatched groups as null in the vec-shaped preg_*

preg_match_all() and preg_match_all_set_order() were the last preg_*
functions handing back a bare Vec<String>, where a group that did not
participate is indistinguishable from one that captured "". Hand back
Option<String> as the map-shaped functions already do; php_match_row(),
the last of the truncate-then-pad helpers, goes with them.

preg_split_delim_capture() keeps its Vec<String>. preg_split() accepts
no PREG_UNMATCHED_AS_NULL, so there is no null form to move it to, and
its result interleaves split segments -- which can never be absent --
with the captured delimiters.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions