[TASK] Integrate Flow Package Subpackage

In order to enable the Package Management API, the used Flow classes
have been placed in the core. The last synced state and the made
changes to the source are noted in a README file.

Resolves: #52737
Related: #47018
Releases: 6.2
Change-Id: Ic8fda623d9ff81f52c3c104a0d5ae7c290bf7953
Reviewed-on: https://review.typo3.org/24666
Reviewed-by: Alexander Opitz
Tested-by: Alexander Opitz
Reviewed-by: Sascha Egerer
Tested-by: Sascha Egerer
Reviewed-by: Thomas Maroschik
Tested-by: Thomas Maroschik