[TASK] Remove @internal for MfaProvider classes

The following classes were marked as @internal in TYPO3 11 since
the feature was experimental. This should have been removed with
TYPO3 12. The @internal has now been removed for:
\TYPO3\CMS\Core\Authentication\Mfa\MfaProviderInterface
\TYPO3\CMS\Core\Authentication\Mfa\MfaProviderPropertyManager
\TYPO3\CMS\Core\Authentication\Mfa\MfaViewType

Resolves: #101237
Related: #100224
Related: #93526
Releases: main, 12.4, 11.5
Change-Id: Iad9b3337a595c2ee1b9162f4cd1463d3c45881f1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79716


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>