[TASK] Enhance documentation of CountrySelectViewHelper

Related: #99618
Resolves: #99788
Releases: main
Change-Id: I826a40e306a77403dd06270eb83f5131920c219d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77661


Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>