Add some more comments to TemplateService related
properties and fix typos.

Resolves: #97796
Releases: main
Change-Id: I131e141e0d1acce57ded287348c7ed0e2ab8a983
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74964

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