XTCE12 — MetaCommandStep argument assignment

MetaCommandStep argument values are assigned using <ArgumentList> / <Argument> elements. Using these elements creates two issues in the XTCE model:

1. Two different element definitions for <ArgumentList> / <Argument>
   1. <MetaCommandStep> / <ArgumentList> / <Argument>
   2. <MetaCommand> / <ArgumentList> / <Argument>
2. Two XML implementations of the ArgumentAssignment concept:
   1. <MetaCommandStep> / <ArgumentList> / <Argument>
   2. <BaseMetaCommand> / <ArgumentAssignmentList> / <ArgumentAssignment>

Recommend replacing the argument assignment elements in <MetaCommandStep> with the elements used for <BaseMetaCommand>.
This would provide a more unified and descriptive definition.

Use ArgumentAssignmentList

In the complexType MetaCommandStepType, add the annotation:
<annotation>
<documentation>Describe a MetaCommand step, consisting MetaCommand reference and argument list. See MetaCommandStepListType and NameReferenceType.</documentation>
</annotation>

and replace the element:
<element name="ArgumentList" type="xtce:ArgumentValueAssignmentListType" minOccurs="0"/>
with:
<element name="ArgumentAssignmentList" type="xtce:ArgumentAssignmentListType" minOccurs="0"/>