Multiline legend items

[chicio]

Hi,

as discussed in #169,I tried to add multiline support for legend items with long names. I used tspan as discussed and some dynamic height calculations (based on the bounding box (getBBox) + getComputedTextLength).
It works as expected. The items lines are aligned after the legend number.

There is still room for improvement, because we should be able to calculate the entire structure of the legends dynamically. Anyway for now, if a legend list of items is too long we should play with the parameters I added the previous PRs to fix the offset (in particular the legends offsets).
Attached you can find some example:

• the Zalando tech radar rendered, where we have an example of an item going on 2 lines
• the a video + a zip containing a working example of the Lastminute tech radar where we have a lot more items (and a lot of them going on 2 lines). Basically you can see from the code that by playing with the offset you can have "infinity legends".

I tested it carefully, but please do all the checks that you want/need on your side, and let me know if this PR makes sense and can be useful (like the previous one).

lastminute-tech-radar-example-video-720.mov

lastminute-tech-radar-example-code.zip

[bocytko]

Thanks for the PR. It's a busy week for us (Cyber Week/Black Friday), so realistically I can take a look at this earliest next week.

[chicio]

@bocytko sure, no problem.
Take you're time (this week is a busy one for everyone working in online retail company I guess😅)