Support the new Azure SQL regular expression functions

[See announcement here](https://devblogs.microsoft.com/azure-sql/introducing-regular-expression-regex-support-in-azure-sql-db/#:~:text=REGEXP_LIKE%3A%20This%20function%20returns%20TRUE,pattern%20matches%20in%20a%20string.); this is still in private preview.

We should be able to translate the standard Regex APIs to at least some of these (similar to what we already do for PG and SQLite), and possibly introduce EF.Functions if needed for others.