[FEATURE] Allow `Configuration/user.tsconfig`

Similar to `Configuration/page.tsconfig`,
default User TSconfig is now loaded from
extensions `Configuration/user.tsconfig` files.

ExtensionManagementUtility::addUserTSConfig()
is deprecated similar to the page TSconfig
patch from #101799.

Resolves: #101807
Related: #96614
Related: #101799
Releases: main
Change-Id: I11cb1a05b8a582ca8f2937077fefa810e36b92d4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80767


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Stephan Großberndt <stephan.grossberndt@typo3.org>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan B�rk <stefan@buerk.tech>
Reviewed-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>