OPSMN-5187: In case of multi-select PV dropdown field, the selected values were being added to the default PVs list irrespective of whether they were present or not. This caused the same PV to appear twice in the dropdown widget.
OPSMN-5187: In case of multi-select PV dropdown field, the selected values
were being added to the default PVs list irrespective of whether they
were present or not. This caused the same PV to appear twice in the dropdown
widget.

Fixed the dropdown widget to ensure the selected values are added only if
they are not present in the default PVs list.

krishagni/openspecimen,krishagni/openspecimen,krishagni/openspecimen