Fixed TokenTroubleshooting for CesiumGeoJsonDocumentRasterOverlay

[gojushin]

Description

tldr:

Clicking "Troubleshoot Token" on a CesiumGeoJsonDocumentRasterOverlay Component causes a NullReferenceException, because of a missing Implementation.

non-tldr:

The main root of the issue lies in a missing implementation inside the getServer function of IonTokenTroubleshootingWindowImpl.cpp.

When the CesiumIonAsset used in the window is created, this constructor is called:

public CesiumIonAsset(CesiumGeoJsonDocumentRasterOverlay overlay)
{
    this._type = AssetType.GeoJsonOverlay;
    this._geoJsonOverlay = overlay;
}

Consequently, getServer returns a nullptr in the final else block because both asset.tileset and asset.overlay are never set.
However, the constructor in CesiumIonAsset.cs specifically sets the _geoJsonOverlay variable (which has a public getter), which we can use here.

(This follows the same pattern as _tileset and _overlay)

So. Eventually, the issue can be fixed by adding a check for asset.geoJsonOverlay (and adding it to ConfigureReinteropEditor.cs's ExposeToCPP of course).

Issue number or link

I very briefly mentioned this bug here

Author checklist

• I have submitted a Contributor License Agreement (only needed once).
• I have done a full self-review of my code.
• I have updated CHANGES.md with a short summary of my change (for user-facing changes).
  (However, I wasn't sure where to put it, so I just added it to the latest changes....😅)
• I have added or updated unit tests to ensure consistent code coverage as necessary.
• I have updated the documentation as necessary.

Testing plan

In the current version of the plugin clicking "Troubleshoot Token" on a CesiumGeoJsonDocumentRasterOverlay Component causes a NullReferenceException.

After implementing the fix, everything works as expected.