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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fill_layer_combo(self):
 """Fill layer combobox."""

        project = QgsProject.instance()
        # MapLayers returns a QMap<QString id, QgsMapLayer layer>
        layers = list(project.mapLayers().values())

        extensions = tuple(extension_siblings.keys())
        for layer in layers:
            if layer.source().lower().endswith(extensions):
                icon = layer_icon(layer)
                self.layers.addItem(icon, layer.name(), layer.id())