Refactor ext/pgsql test

[KentarouTakeda]

I refactored the ext/pgsql tests based on some recent pull requests.
The content and results remain unchanged. This is just an internal improvement.

With this refactoring, we can expect the following benefits:

• Test independence:
  Some tests were dependent on the execution order of previous and subsequent tests.
  All tests can now be executed independently.
• Test parallelism
  One test no longer interferes with another. All tests can be run in parallel.

Specifically, i made the following modifications: For readability, each modification is fixed in a separate commit.

• Use --CLEAN-- to delete objects at the end of the test.
  faabc3f
• Moved *.inc to another folder to make filenames easier to read.
  7b507cd
• Tables used for tests are defined for each test instead of being set all at once in config.inc
  002fe32 293b0b0
• Use different object names for each test. The name is based on the test file name.
  002fe32 5ab45c7

Ref:

• Improve ext/pdo_pgsql tests cleanup #11855
• Improve ext/pdo_mysql tests cleanup #11879
• [Test] Optimized pdo_mysql tests #12555

[Girgias]

Thank you for working on this!

It has been very annoying to need to run these tests sequentially.

Could you always use uppercase letters for SQL keywords, and CLEAN sections should use an IF EXISTS clause as the table may not be created in the test.

[KentarouTakeda]

Could you always use uppercase letters for SQL keywords,

Fixed in 21e61ad

All existing code unrelated to this pull request was also fixed.
However, there were some inconsistencies in the interpretation of what should be treated as "SQL keywords". For those, I respect the original code and have not fixed it.

[Girgias]

Looks mostly good now! Only a couple of nits and questions. :)

[KentarouTakeda]

@Girgias
Your very detailed review helped me a lot!
I have corrected each of the points pointed out. thank you.

[Girgias]

One final remark and good to merge :)

[Girgias]

Thank you!