Add additional tests for getTablePrivileges() for materialized views and foreign tables

[sehrope]

Placeholder issue for adding additional test cases for materialized views and foreign tables. See #2049 for details.

This should be straight forward to add would be great first time contribution as it's totally isolated in new test code.

[mgrobaker]

Could you elaborate on this a little? I am working on this as my first issue. I've gotten everything up and running, and all tests are passing. I'm now in this test class and trying to work on the issue itself.

Two questions off the top of my head - but feel free to add extra color as well

1. Are there existing tests already in here that I can use as a basis for making new methods to test the views and foreign tables? Or is that part of the issue, coming up with such tests.
   (It is a little hard for me to read through the whole class DatabaseMetaDataTest, given that there are several database objects being tested and not a ton of comments. But I can do that. I just wanted to check that was necessary before going through it all.)

2. Also, the title of the issue speaks to getTablePrivileges(). I don't exactly understand why. I see getViewPrivileges() was added. Is the idea to beef up the tests in just this specific method, or to make new methods to test just privileges on views and foreign tables?

[sehrope]

That PR fixed a bug where the getTablePrivileges(...) metadata method was only returning results for tables and partitioned tables, but not views, materialized views, and foreign tables. The fix included all of those relation types but the additional test only covered views with the new testViewPrivileges() method.

The PR I'm suggesting someone create would be two parts:

1. Add testMaterializedViewPrivileges() which would create a materalized view, verify that it appears in getTablePrivileges(), and then drop the materialized view in the teardown.
2. Add testForeignTablePrivileges() which would do the same with a foreign table.

That second one is a bit more complicated as a foreign table quite a bit more plumbing to get set up (an fdw, a foreign server, etc). So I'd suggest just doing just the materialized view piece.

[mgrobaker]

Got it, thanks - this is clear now

[mgrobaker]

Opened the PR. As you suggested, it just adds testMaterializedViewPrivileges()

I can take a pass at testForeignTablePrivileges() as well. Just let me know if that will be in a new issue. If I can't figure it out then I'll have to leave for someone else.