[Feature]: Implement ViewpointDefinitionExtensions

[samatstariongroup]

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of the SysML2.NET
• I have searched open and closed issues to ensure it has not already been reported

Description

The ViewpointDefinitionExtensions class in SysML2.NET/Extend/ViewpointDefinitionExtensions.cs contains 1 extension method(s) that compute derived properties for the IViewpointDefinition interface. These methods currently throw NotSupportedException and need to be implemented.

Checklist

• List<IPartUsage> ComputeViewpointStakeholder(this IViewpointDefinition)

System Configuration

• SysML2.NET version: 0.19.0
• Source file: SysML2.NET/Extend/ViewpointDefinitionExtensions.cs