Fix Split Strips operator not showing shortcut

This is because the menu entry was using different operator
properties from what the shortcut is defined for. It was needed
to make it so an operator which is called from the menu does not
have dependency on the mouse location.

Now it is achieved by resolving MOUSE side to RIGHT from the
operator's exec().

Ref #112598

Pull Request: https://projects.blender.org/blender/blender/pulls/113143