VARCHAR(MAX) SQL Server type should be introspected to TEXT

### Feature Request

#### What & Why

`VARCHAR(MAX)` and `NVARCHAR(MAX)` represents `text` (large text) DBAL type in SQL Server.

The same for `VARBINARY(MAX)`, it represents `blob` DBAL type.

#### How

If the introspected length is `MAX`, introspect the type as `text`/`blob`.