Support for N1QL Pattern-matching functions (regex)

Provide support for N1QL regex expressions via REGEXP_CONTAINS(expression, pattern)

https://docs.couchbase.com/server/5.5/n1ql/n1ql-language-reference/patternmatchingfun.html

Start with the Couchbase N1QL pattern-matching documentation linked in the issue and inspect the repository’s LINQ-to-N1QL translation entry points to determine how REGEXP_CONTAINS should be exposed. Done means LINQ queries can produce the requested N1QL regex expression and the behavior is covered by the relevant existing tests.

Written by the indexing model from the issue text.