Importing d3.mouse via module instead of via <script/> reference on m…

[mebrein]

I use the cubism esm module now via a React useEffect hook. When import the mouse function via the module system, it doesn't throw anymore.

[BigFatDog]

Thank you for this PR. I'll try to finish review this week.

[BigFatDog]

I've tested your code via running npm run dev
stock.html prints error:

Uncaught TypeError: Cannot read property 'sourceEvent' of null

This is exactly the issue I had when I tried to use mouse in a modular approach. After some investigation, I think it might be an issue with d3-selection's packaging process with rollup. I have no solution for this.

To get rid of this issue, one possible solution is to add d3 to your global namespace via webpack:

    new webpack.ProvidePlugin({
        d3: 'd3',
    }),