feat(#85): expose selectedIndexes to tooltip renderer

[canastro]

This is a proposal to #85 and it's a breaking change:

Context

In our app we are using a tooltipRenderer but we need to be able to customize the display of each field on the tooltip based on information we dont have available in the tuples that are provided to Graphic. Therefore we need to get back the "index" of the selected tuple so that I can get the appropriate record from our data structure. Thats the gist of what we need.

To give a bit more context, we're dynamically creating charts in a spreadsheet application with data provided by the user and, as google sheets we want to allow the user to have values with different formatting in each point.

Here is an example where the user defined different number of decimal places per cell via formatting, ie. the user did not introduce 1.000000, the actual value is "1" but the formatting is "use 6 decimal places => 1.000000":

Screen.Recording.2022-04-17.at.08.37.53.mov

Proposal

In the tooltipRenderer return back the "selectedIndexes" to allow the user to find the appropriate record on a more complex datastructure on user-land. For users not using "tooltipRenderer", provide "tooltipFieldFormatter" which receives the selectedIndex for the current tuple being formatted.

Let me know what you think of the overall approach and if there are any alternative ways of doing this.

Thank you.

[entronad]

1. To add the selectedIndexes is a good idea. With it, you can find your original datum, and make usage of it's special attributes which are not in the tuples. There are some conflicts of this PR, so for convenience I will add it myself.
2. I don't think "tooltipFieldFormatter" is a good idea. It's function are all covered by the renderer, and it's hard to get what this argument really means. (I got the meaning of "field formatter" only after I carefully read the source code.). So, with the scale.formatter for common users, and renderer for senior users, I think the tooltipFieldFormatter is not that necessary.

[canastro]

Alright, makes sense. I’ll review the PR and I’ll let you know when it’s ready for further review

[canastro]

@entronad I misread the part for convenience I will add it myself. and rebased and simplified this PR.
Feel free to ignore this PR and close it if you're already working on it.

[canastro]

I haven't created any example for the selectedIndexes, let me know if you want me to add one.

[entronad]

Added in v0.10.0.