RepresentationInstances: IFC support

[katehryhorenko]

BACKGROUND:
In prev. PR I added multiple representations. So GeometricElement now has list of RepresentationInstances. This PR contains changes inside IFC serializer that allow to include all SolidRepresentations that are marked as "default" to IFC

DESCRIPTION:

• Small refactoring: AddSolidOperationToDocument method encapsulates the old logic of adding the solid operation to IFC document
• All SolidOperations that are marked as "Default" are serialized to IFC

TESTING:

• I tested it with Unicorn function. I created a test with IFC creation. If you want, I can share Unicorn function with you. But you can create any function and create RepresentationInstances instead of Representation inside UpdateRepresentations method.

REQUIRED:

• All changes are up to date in CHANGELOG.md.

COMMENTS:

• Any other notes.

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This change is 

[anthonie-kramer]

Just one comment about possible null value, but :

Reviewed all commit messages.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @katehryhorenko)

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Elements.Serialization.IFC/src/Serialization/IFC/IFCElementExtensions.cs line 97 at r1 (raw file):

                                foreach (var geom in ifcRepresentations)
                                {
                                    var styledItem = new IfcStyledItem(geom, styleAssignments[representationInstance.Material.Id], null);

Can the Material be null in RepresentationInstance? If so, we should use a TryGetValue() for the representationInstance.Material?.Id

[katehryhorenko]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @anthonie-kramer)

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Elements.Serialization.IFC/src/Serialization/IFC/IFCElementExtensions.cs line 97 at r1 (raw file):

Previously, anthonie-kramer (Anthonie Kramer) wrote…

Can the Material be null in RepresentationInstance? If so, we should use a TryGetValue() for the representationInstance.Material?.Id

Done.