dual axes and default

[todo]

antv-spec/src/adaptor/g2plot/toConfig.ts

Lines 45 to 50 in f18179e

	// TODO: dual axes and default
	return '';
	}
	export function toG2PlotConfg(spec: ChartAntVSpec) {
	const config: Record<string, any> = {};

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This issue was generated by todo based on a TODO comment in f18179e when #9 was merged. cc @antvis.