[DOCS] Explain that L10n signal/slot is not affected

The breaking change documentation is adapted to explicitly mention that
the signal/slot registration is kept untouched.

This will prevent confusion for developers reading the list of breaking changes.

Related: #50467
Related: #62983
Related: #84131
Related: #84691
Releases: master
Change-Id: I43ff5a6882e84c29844495fa9f10e6a35f07b1ff
Reviewed-on: https://review.typo3.org/58313


Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>