Add regexp function - regexp_matches()

### Is your feature request related to a problem or challenge?

_No response_

### Describe the solution you'd like

regexp_match() is already implemented, so we just need to look into building on that.

### Describe alternatives you've considered

_No response_

### Additional context

Discussed in #11946

Start by locating the existing regexp_match() implementation and read the discussion in issue #11946 to determine the expected behavior for regexp_matches(). Add the new function once its semantics are clear, and verify that it is available and behaves as agreed in the relevant query-engine tests.

Written by the indexing model from the issue text.