QmlDesigner: Reset quick3D importer between each file

Quick3D importer caches various things when it does the import, making
reusing the instance for multiple imports error prone.

Change-Id: I6e8e3dedf579683cdda58624172395a392f4e567
Fixes: QDS-1960
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/qmldesigner/components/itemlibrary/itemlibraryassetimporter.cpp

@@ -315,6 +315,9 @@ void ItemLibraryAssetImporter::parseQuick3DAsset(const QString &file, const QVar
         return;
     }
 
+    // The importer is reset after every import to avoid issues with it caching various things
+    m_quick3DAssetImporter.reset(new QSSGAssetImportManager);
+
     if (originalAssetName != assetName) {
         // Fix the generated qml file name
         const QString assetQml = originalAssetName + ".qml";