[TASK] Move classAliasMaps into compatibility6 extension part 1

Change-Id: I5845baff737e739599cf29847981f56f5cf866e3
Resolves: #62026
Relates: #62013
Releases: master
Reviewed-on: http://review.typo3.org/33150
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>