Feature: #101807 - Automatic inclusion of User TSconfig of extensions

See forge#101807

Description

Extension authors can now put a file named Configuration/user.tsconfig in their extension folder.

This file is then recognized to load the contents as global User TSconfig for the whole TYPO3 installation during build-time. This is more performant than the existing solution using ExtensionManagementUtility::addUserTSConfig() in ext_localconf.php, which is added to $TYPO3_CONF_VARS[SYS][defaultUserTSconfig] during runtime.

Impact

When a file is created, the User TSconfig is loaded automatically without a custom registration, cached within the Core caches, and more performant than the existing registration format. The old registration format has been been marked as deprecated, see Deprecated ExtensionManagementUtility::addUserTSConfig() for more details.