[compat2021] Link to wpt.fyi run at the point of the graph

[foolip]

On https://wpt.fyi/compat2021?feature=position-sticky, clicking a point in the graph will show a "show browser changelog" link. It would be very useful to also have a list to the wpt.fyi run which is being that point in the graph, and maybe a diff against the previous run.

This would make it easier to figure out why regressions have happened, as in the What is causing the score reduction for position:sticky? thread.

[foolip]

@stephenmcgruer do you think this would be easy to fix?

[stephenmcgruer]

Annoyingly not trivial, because I dropped the sha from the new unified csv file.

You'd need to:

1. Add it to the csv file generated here: https://github.com/Ecosystem-Infra/wpt-results-analysis/blob/main/compat-2021/main.js#L390
2. Create a sha list here, similar to browserVersions - https://github.com/web-platform-tests/wpt.fyi/blob/main/webapp/components/compat-2021.js#L87
3. Modify this tooltip action to use the new shas list - https://github.com/web-platform-tests/wpt.fyi/blob/main/webapp/components/compat-2021.js#L682

The most annoying bit will be not breaking wpt.fyi when you add the SHAs to the csv file (yay csv files... wish I'd used JSON?)

[foolip]

Thanks Stephen! Seems doable but not trivial then :)