Regexp subexpression replacement doesn't work, throws exception

[njx]

1. In Getting Started, Edit > Replace
2. Enter /<([^>]+)>/ as the query and hit enter
3. Replace with [$1]
4. Click Yes

Result: Find bar disappears and there's an exception in the console.
Expected: Either we should properly handle the subexpression substitution, or we should just replace with "$1" and continue.

[njx]

It looks like there's code in FindReplace to deal with regexp subexpression substitutions, but the match data from the regexp doesn't get properly passed to it (in either the single-replace or replace-all cases). Seems like it shouldn't be that hard to hook it up, but either way we shouldn't be silently failing.

[njx]

BTW, this isn't a recent regression--it doesn't work as far back as Sprint 25. Perhaps it never worked.

[peterflynn]

Reviewed. Assigned @njx to review potential fix in PR #5295.