[!!!][TASK] Migrate backend_layout.icon to FAL

The last place in TYPO3 Core to use internal_type=file (backend_layout.icon)
is now moved to FAL with sys_file_reference.

An upgrade wizard is in place to migrate existing icons from uploads/media
to sys_file.

FormEngine is migrated to also allow to use sys_file_references for the
TCA ctrl property "selicon_field".

With this change, a followup could be integrated to deprecate "old-style"
internal_type=file code, and also to not create the uploads/ folder at all anymore
within TYPO3 installations.

Additionally, the functionality of "selicon_field_path" should be deprecated
in the future.

Resolves: #83153
Releases: master
Change-Id: I578fd68b7e1f7bc6a1991b90e7750b903d3ec28b
Reviewed-on: https://review.typo3.org/54830


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Sebastian Hofer <sebastian.hofer@marit.ag>
Tested-by: Sebastian Hofer <sebastian.hofer@marit.ag>
Reviewed-by: Pawel Cieslik <p.cieslik@macopedia.pl>
Tested-by: Pawel Cieslik <p.cieslik@macopedia.pl>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>