[DBAL-830] Fix SQL Server default constraint name generation for quoted identifiers

This is a replacement for https://github.com/doctrine/dbal/pull/539.
It makes the generation of default constraint names consistent for quoted and unquoted identifiers by always unquoting them before generating the hash. This is the only possibility to ensure that the same hash is always generated for the same identifiers.
Unfortunately this introduces a minor BC break for existing applications that use either reserved keywords or explicitly quoted identifiers for columns with a declared default value and want to alter those columns in the future. It will generate `DROP CONSTRAINT` / `ADD CONSTRAINT` statements with different contraint names for the first time for a table alteration on existing v2.4 schemas.