src/vs/workbench/api/common/extHostLanguageFeatures.ts/TypeHierarchyAdapter/_cacheAndConvertItem
class TypeHierarchyAdapter:	private _cacheAndConvertItem(sessionId: string, item: vscode.TypeHierarchyItem): extHostProtocol.ITypeHierarchyItemDto {
		const map = this._cache.get(sessionId)!;
		const dto = typeConvert.TypeHierarchyItem.from(item, sessionId, map.size.toString(36));
		map.set(dto._itemId, item);
		return dto;
	}