Generalize SQLite paren counting to fix PG CHECK constraint parsing

Generalize SQLite paren counting to fix PG CHECK constraint parsing

Fixed reflection of PostgreSQL CHECK constraints where an expression made
up of multiple parenthesized sub-expressions, such as ``(x IS NULL OR y IS
NULL) AND (x IS NULL OR y IS NULL)``, would have its leading and trailing
parentheses incorrectly stripped, producing an unbalanced and
syntactically invalid reflected expression.  Pull request courtesy
Shaurya Singh.

Fixes #13157
Closes: #13303
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/13303
Pull-request-sha: 79bb5f3855ab434d9110864bc467bda66de08a2c

Change-Id: I8312a82527b39aeade731fa358cf7d1959e32427