[FEATURE] Allow deleting IRRE elements via `postMessage()`

To invoke a deletion on items in FormEngine's Inline Relation container
API-wise, a new message identifier `typo3:foreignRelation:delete` has
been introduced.

Resolves: #102836
Releases: main
Change-Id: I6627beb8bfa61be71239ed80e060e66163bc812a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82594


Tested-by: Daniel Siepmann <coding@daniel-siepmann.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>
Reviewed-by: Daniel Siepmann <coding@daniel-siepmann.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>