Add a "Clear Custom Split Normal Data" in the clean-up menu

There have been some requests over the years for a way to Clear Custom Split Normal Data from ALL Selected objects. Right now, the operator only takes into account the active object.

My proposition is to either make it work for all selected objects is clicked whil holding Alt. Or in the menu Object>Clean Up>Clear Custom Split Normal Data

The use cases is for projects that have many objects imported from other format, and said objects need to keep their shared data, materials, etc. In that case, joining all together, clearing, and splitting again would loose too much information.