Cloning a field clones field contents as well

When clicking _\+ Add New_ to add a field when `'multiple' => true`, the cloned field's contents are copied into the new field:


The expected behaviour (in my mind) would be that a new blank field would be created like so:


Start by reproducing the issue in the custom-field interface with “multiple” enabled and clicking “+ Add New” to identify the handler that clones the field. Trace how the existing field contents are copied, then verify that the newly added field is blank while the original remains unchanged.

Written by the indexing model from the issue text.