[TASK] Initialize datepicker JS in external file

Before this patch, the DatePickerViewHelper of EXT:form would
always render its datepicker JavaScript inline.

The DatePickerViewHelper now includes an external JS file for the
initialization which is not utilizing any dynamically generated
parts anymore.

Resolves: #90264
Releases: master
Change-Id: I1f72690d41121dc0cd48a2db55de883fe84589c8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63263


Tested-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>