[BUGFIX] Fix functional tests for EXT:impexp on PostgreSQL

Introduce dedicated fixures for the export data based on the database
platform being tested. Due to mysqlnd and PDO based drivers returning
different types of values (mainly int vs string) the resulting XML
is dependent on the database.

Change-Id: I776cfbc28c7355e72c21fa89097077f94225e223
Resolves: #79798
Releases: master
Reviewed-on: https://review.typo3.org/51774


Reviewed-by: Manuel Selbach <manuel_selbach@yahoo.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>