[BUGFIX] Implement deferred BE image processing consistently

Change the implementation of backend deferred image processing
to use a file processor, which is only but always used in the backend.

By doing so all limitations of the current implementation are resolved,
which means, width and height of the image can be set in HTML, to avoid
layout shifts and once the images are processed, they will simply
be delivered by the web server.

Inconsistencies with thumbnail ratio (depending on crop being defined
or not) are also tackled on the go.

While this changes processing configuration for some files,
which triggers a re-generation, it should not matter, as image
processing will be done in parallel on request, making such changes
viable in a bugfix release.

The introduced database field is neither used nor required for the
current implementation, but is introduced to provide a possibility for
third party processors to replace the current implementation with simple
(and persisted) URLs to third party SaaS image processing services.

Resolves: #92188
Releases: master, 10.4
Change-Id: I8d1e14324085c5b6ba646475206c8cb10a1fc10d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/65237


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>