addEntities method
Add entities to the DXF object
Implementation
void addEntities(AcDbEntity entity) {
entity._handle = _headerSection._nextHandle.toRadixString(16);
var result = entity._groupCodes.firstWhere((element) => element.code == 5);
result.value = entity._handle;
_entitiesSection._addEntity(entity);
_headerSection._increase();
}