expr: fix regex matching on inputs containing newlines

[ChrisDryden]

I was investigating the onig flags to see what is missing with the multiline related options to achieve gnu compatibility and I found that there was a RegexOptions::REGEX_OPTION_MULTILINE and when testing adding it to all of the places where the regex options singleline was added it matched the missing multiline regexes that were previously failing

Fixes: #10542

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/shuf/shuf-reservoir (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/sort/sort-stale-thread-mem (fails in this run but passes in the 'main' branch)

[sylvestre]

the ci isn't happy

[ChrisDryden]

It's all flakiness :(

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/basenc/bounded-memory is now passing!

[cakebaker]

Thanks!