[BUGFIX] Enable overriding header of backend preview again

Since commit e09082f7 (v10 release) the possibility to override the
preview header was gone. This patch moves the drawItem hook out of
the renderPageModulePreviewContent method to be able to pass the before
rendered previewHeader to it.

Resolves: #91760
Relates: #90906
Releases: master
Change-Id: Ia7d29333543d764f4ebaec0330df1817032dc8fe
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/68953


Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>