Fix postgres mixedcase database (#1800)

[beckjake]

Fixes #1800

Fix mixed-case database handling on postgres (and presumably redshift) with two changes:

• when listing the catalog, do not re-case the database but instead render it as given
• use the information_schema.database value for the built relation rather than the lowercased form

I disabled the new test on Windows, it's just too painful to play run-break-fix on configuring stuff without a local Windows development env to test on.

[drewbanin]

Works great! Can you update the changelog accordingly?

Under the pg/redshift heading:

- Fix for internal errors when run against mixed-case logical databases (#1800, #1936)

Pending that, approved

[beckjake]

I'm going to merge this even though snowflake timed out on Windows - it's just information_schema queries taking forever again.