DBAL-54 was fixed in commit 3d55dc8e by
changing SQL queries order. However it was later reintroduced.

This patch uses a different, more future-proof way, approach by using
DROP SEQUENCE ... CASCADE syntax, and thus does not depend on queries order.

[DBAL-374] Fix issue with column quoting in primary keys, fixing this in indexes in general is much more complex as the code is messy.

This will only happen when adding primary keys via ALTER TABLE

Default table collation changed to `utf8_unicode_ci`, as it handles properly a much wider array of characters (Cyrillic, for example) at a generally negligible cost of performance.

[DBAL-178] Fixed an undescriptive error message and a problem when using custom types and their reverse engineering from the database. Allows Type#getMappedDatabaseTypes() to be implemented in custom types, mapping to vendor database types during reverse engineering.

Fix the repeat calling of getReservedKeywordsClass() that causes a considerable slow down when running lots of migrations.

SQL Server doesn't like the quoted alias for doctrine_rownum and fails when setting setMaxResults() and setFirstResult() in query, returning an error like "Conversion failed when converting the varchar value 'doctrine_rownum' to data type int. (severity 16)"