[TASK] Check for libxml bug in install tool

Add check for libxml bug when saving special characters ">><<"
in a flexform

Resolves: #51271
Releases: 6.2
Change-Id: I5d120cdfeb9538209273c8761d017cb67256617b
Reviewed-on: https://review.typo3.org/25089
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Oliver Klee
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind