[TASK] oncontextmenu: Avoid duplicating onclick-functionality

Where onclick and oncontextmenu behave the same avoid duplicating
JavaScript-code and simply call the click()-functionality.

Change-Id: Iaa0b96fd311ea1a8367ef474b483e6c92bb1bcff
Resolves: #54288
Releases: 6.2
Reviewed-on: https://review.typo3.org/26094
Reviewed-by: Frans Saris
Tested-by: Frans Saris
Reviewed-by: Markus Klein
Tested-by: Markus Klein