[BUGFIX] Use push parser instead of pull parser on fetching extension list

Issue #75022 reported problems with libxml and operations on compressed
file streams. The work around for that patch showed drawbacks with memory
consumption. That's why the push parser is used as default now.

Resolves: #75721
Related: #75022
Releases: master, 7.6, 6.2
Change-Id: I6daadd4b375634cf45272bb249e4bfa083f03646
Reviewed-on: https://review.typo3.org/48189


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>