feat: Use transactional DDL rollback, to perform view comparison for postgres.

[DanCardin]

I.e. actually create the view (in a transaction) and roll it back to see what the rendered version of the view would be, in order to get an exact comparison between two views.

This can only be safely done in a database that has transaction DDL, like postgres and unlike mysql.

[coveralls]

Pull Request Test Coverage Report for Build 4276300803

• 35 of 35 (100.0%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 96.546%

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Totals
Change from base Build 4275908533:	0.03%
Covered Lines:	1571
Relevant Lines:	1625

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💛 - Coveralls