[BUGFIX] Replace ###CURRENT_PID### with value from DB within FlexForms

Replace ###CURRENT_PID### in FlexForm context with values from
database. Within FlexForm context these values need to be
retrieved from the key flexParentDatabaseRow.

Resolves: #76888
Releases: master, 7.6
Change-Id: I5fd3cb0a18e41ae0d15cbb44556d05d88506a093
Reviewed-on: https://review.typo3.org/48749


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Ralf Merz <info@merzilla.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Sebastian Fischer <typo3@evoweb.de>
Tested-by: Ralf Merz <info@merzilla.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>