Use BackendUtility::getPagesTSconfig in TSFE when getting tsconfig
Inside the TypoScriptFrontendController the method getPagesTSconfig is used to get the tsconfig from page records. Both via the TSconfig fields but also "included" tsconfig.
The method consist of the same code as BackendUtility::getRawPagesTSconfig (which is called by getPagesTSconfig) - the main difference is, that the frontend method doesn't call emit the signal GetPagesTSconfigPreIncludeSignal to have extensions auto include. So, this gives a different functionality from backend to frontend.
A usecase is inclusion of gridelements layouts. This is used in the frontend for rendering. But when TSFE gets the tsconfig, the signal is not emitted and the tsconfig is not being filled with the layout configuration like it does in the backend