[BUGFIX] Display human-readable preview of FlexForm values

This change transforms the processed record of FlexForms
into a human-readable format.

This is especially useful when comparing changes in the
history module or the workspaces diff view.

The diff needs to be formatted with line breaks and tabs as
the output is passed through "htmlspecialchars" before it
will be displayed.

The white-space css setting needs to be changed to
"pre-wrap", because this is the only setting where line
breaks and tabs are kept and the text will still be
word-wrapped.

Resolves: #91148
Releases: main, 12.4
Change-Id: I189555f459a3a96594e9c708b4ee71c908efd970
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75117


Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81508