[BUGFIX] Wrong name attribute in custom user rendered items

Configuration items/properties that use a user function to
render the accordant values and possibilities (like, e.g.
saltedpasswords does in the Core) have a wrong name attribute.

The information to be delivered shall be:
* fieldName: Extbase prefixed form name
* fieldValue: the value of the field to be shown
* propertyName: Name of the property, e.g. "some.setting"

Change-Id: I19a11b20b9a897632e17c6bd9919d8cd6fe0b155
Fixes: #39958
Releases: 6.0
Reviewed-on: http://review.typo3.org/13918
Reviewed-by: Wouter Wolters
Reviewed-by: Susanne Moog
Tested-by: Susanne Moog
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn