Fix convert_tz function in Postgresql

[mesolaries]

$toTz parameter was passed before $fromTz. It causes convert_tz function to work not as expected. This pr fixes this bug.

[mesolaries]

@x86demon please review

[paulferrett]

@x86demon This issue tripped me up for quite a while as well.

[x86demon]

@mesolaries thank you for your PR and fix. Please update tests to show the bug and correctness of the fix.

Sorry for delay in the answer.

[x86demon]

I've checked CONVERT_TZ and it works as expected. As a source of this implementation MySQL CONVERT_TZ was taken. https://dev.mysql.com/doc/refman/8.0/en/date-and-time-functions.html#function_convert-tz DQL function should return same results for both supported platforms (MySQL and PostgreSQL) I've used next example MySQL

mysql> SELECT CONVERT_TZ('2004-01-01 12:00:00','UTC','Europe/Kiev');
+-------------------------------------------------------+
| CONVERT_TZ('2004-01-01 12:00:00','UTC','Europe/Kiev') |
+-------------------------------------------------------+
| 2004-01-01 14:00:00                                   |
+-------------------------------------------------------+

Current implementation for PostgreSQL

postgres=# SELECT "timestamp"('2004-01-01 12:00:00' AT TIME ZONE 'Europe/Kiev' AT TIME ZONE 'UTC');
      timestamp      
---------------------
 2004-01-01 14:00:00

I'm closing the PR

@mesolaries, @paulferrett thank you for paying attention.

[mesolaries]

@x86demon Your example is not the same as current PostgreSQL implementation. Parenthesis are in wrong place. Your example: SELECT "timestamp"('2004-01-01 12:00:00' AT TIME ZONE 'Europe/Kiev' AT TIME ZONE 'UTC'); Actual implementation: SELECT "timestamp"('2004-01-01 12:00:00') AT TIME ZONE 'Europe/Kiev' AT TIME ZONE 'UTC';

https://github.com/oroinc/doctrine-extensions/blob/67eda39d5e94fa25d105c759673bc45a5256798f/src/Oro/ORM/Query/AST/Platform/Functions/Postgresql/ConvertTz.php#L22-L24

So, let's assume I want to convert datetime from UTC timezone to Europe/Kiev timezone. I will take current implementation as example. Expected output: 2004-01-01T14:00:00.000Z

postgres=# SELECT "timestamp"('2004-01-01 12:00:00') AT TIME ZONE 'Europe/Kiev' AT TIME ZONE 'UTC';
      timestamp      
---------------------
2004-01-01T10:00:00.000Z

As you can see the output is wrong. This is because $fromTz parameter is passed after $toTz as I mentioned before.

[x86demon]

@mesolaries you are right, I've missed parentheses position. Please update test so I'll be able to merge the PR