SQLite: Translate Regex.IsMatch()

[bricelam]

We have to register a user-defined function, so maybe it should be behind an off-by-default option: (but since this is a well-known function and it's hard to imagine another implementation, maybe it's OK just to always do it in EF)

options.UseSqlite(connection, x => x.EnableRegex());

It would register this function:

CreateFunction("regexp", (string pattern, string input) => Regex.IsMatch(input, pattern));

This translation would be enabled:

.NET	SQL
Regex.IsMatch(input, pattern)	regexp($pattern, $input)