[TASK] Deprecate insertModuleFunction "$classPath" parameter

Deprecates the need to specify the $classPath when registering a submodule
with ExtensionManagementUtility::insertModuleFunction. Remove the
parameter's usage throughout the system extensions.

Also re-adds the removed include_once that were removed without proper
deprecation before (see #49992).

Resolves: #52594
Releases: 6.2
Change-Id: I090278b8e2e7a15e05b14dca757ae2b8ef1e5fb4
Reviewed-on: https://review.typo3.org/24462
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring