[TASK] Use more native types in the blog extension

Also add a missing property that already had a getter
and setter.

Also drop redundant type annotations and comments.

Used command:
> ./Build/Scripts/runTests.sh -s phpstanGenerateBaseline

Resolves: #98133
Related: #98132
Releases: main
Change-Id: I912d78df2d4f2b94b622c51a632690752dbb165b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75432


Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>