[TASK] Add examples for TCA `file` in FlexForms

This adds new fields to EXT:styleguide for
testing TCA type `file` in FlexForm.

Additionally, this also properly tests
that TcaPreparation is working for `file`
in FlexForm context. This includes the
`columnsOverrides` and `overrideChildTca`
functionality as well as the special
allowed / disallowed evaluation and
corresponding placeholder replacement.

Resolves: #104301
Releases: main
Change-Id: I96b41c95898d6782d362e6a4f9140f5ab5419d62
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85094


Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: Garvin Hicking <gh@faktor-e.de>