[TASK] Use FAL functions for image rendering

Instead of relying on the backward compatiblity layer of the
FrontendContentAdapterService when rendering images with
css_styled_content the render_textpic method is modified so that it
is also be possible to use FAL functions and properties for image
rendering.

The captionsSplit / imageTextSplit constants are removed because
every image has its own properties for that with FAL and they are
not needed any more.

The globalCaption rendering was removed because the captions are now
always attached to a single image.

The longdescURL handling was also removed because the files do not
have this property at the moment and the longdescURL field for
tt_content records is also not visible in the Backend.

Resolves: #53764
Releases: 6.2
Change-Id: I1d9c8ad1d7a498816e724960613818a05d587d4f
Reviewed-on: https://review.typo3.org/25511
Reviewed-by: Markus Klein
Tested-by: Markus Klein
Reviewed-by: Frans Saris
Tested-by: Frans Saris