[FEATURE] Use mod dispatcher for tsconfig_help

Use the backend module dispatcher for the
tsconfig_help extension.

Change-Id: I96fbe53025318601b1db113039091be545b6036e
Resolves: #38080
Releases: 6.0
Reviewed-on: http://review.typo3.org/12090
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn