[!!!][FEATURE] Provide dedicated enum for contextual feedback

To clean up cluttered severity definitions for flash messages and
reports, a new `ContextualFeedback` enum is introduced.

The enum is backed, means it holds actual values, which match the
previously known integer values for severities. An internal
`transform()` method may be used to maintain backward compatibility
where needed and to trigger deprecation notices.

Resolves: #97787
Releases: main
Change-Id: I44b706c929277bc765bf302b2b1d32aa1da31f85
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74925


Tested-by: core-ci <typo3@b13.com>
Tested-by: Frank Nägler <frank.naegler@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Frank Nägler <frank.naegler@typo3.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>