[FEATURE] Emit Signal at the very end of DataPreprocessor::fetchRecord()

Introduces a new signal which can be used to e.g. manipulate the
regTableItems_data array to display that manipulated data in TCEForms.

Resolves: #61711
Releases: master
Change-Id: I9dbc5e039e48b5eeaaf639c79d25e5885d007a78
Reviewed-on: http://review.typo3.org/32862
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>