Add "SI extended" formatting rule for the tick exponents

[dberardi99]

Fixplotly/plotly.py#4787

As suggested by @alexcjohnson in plotly/plotly.py#4787 (comment), a new "SI extended" tick exponents' formatting rule has been added to display numbers in the full SI unit range (10^-30 to 10^30).

In addition, the 20.json mock and its baseline have been modified to show how this new mode works.

[alexcjohnson]

LGTM, thanks @dberardi99! It’ll need a draftlog entry, I’d call it an addition rather than a bug fix. @archmoj I see you have this slotted for the next release after 3.0, sounds reasonable, I’ll defer to you for a final review

[archmoj]

@dberardi99 Could you please resolve the conflicts with master?

[alexshoe]

@emilykl@camdecoster The changes here LGTM. Fixed the merge conflict in src/plots/cartesian/axes.js.

[emilykl]

Left a few suggestions for improving the clarity of the code, but LGTM!

@dberardi99 Please add a new draftlog file in draftlogs/ describing this change.

[emilykl]

Woohoo, thanks @dberardi99 and @alexshoe ! 🎉