Support function type splitChunks

[JSerFeng]

We should support function type configs of splitChunks.

For example,

config = {
    splitChunks: {
	    cacheGroups: {
		    shared: {
			    chunks: "all",
			    test: /shared/,
			    filename: data => `shared-${data.chunk.name || data.chunk.id}.js`,
			    enforce: true
		    },
		    common: {
			    chunks: "all",
			    test: /common/,
			    enforce: true
		    }
	    }
    }
}