First step at fixed label and handle support

[Kilian]

This ended up needing changes in quite a bunch more files than anticipated, and might need other things to update as well but I don't quite have the overview for that.

My feeling is that visbug-label would benefit from the same API as visbug-handle/visbug-hover, where label.position is given el and boundingClientRect is calculated in the web component (and isFixed is determined there too).

Now label needs other plugins to deal with boundingClientRect, while handle just calculates it itself.

[argyleink]

hosted playground https://kilian-labels.glitch.me

[argyleink]

This ended up needing changes in quite a bunch more files than anticipated, and might need other things to update as well but I don't quite have the overview for that.

I'll try to do lots of QA on it. Did touch a lot of files, but we did teach a few components a new trick. You did notice a delta where some components have an updated api and others (label) dont. Agree on the suggestion to have label join the rest 👍

PR overall looks good! Does label.element.css need both position supplied?

[Kilian]

Does label.element.css need both position supplied?

I followed the way the other custom properties were defined in that file but I'm happy with using a fallback there too like I did in another file.

[argyleink]

hm, what should we do with position sticky elements?

[Kilian]

I don't know. Unless we make the labels children of the elements I can't think of a way that doesn't involve adding listeners to everything that's position sticky and getting their position on each scroll.

[argyleink]

i dont have any good answers either. this PR is pending squash and merge until I can do a local build and verify across a few test sites. tests and staging look good tho!