Add support for floating bar chart ([start, end])

[gwyneblaidd]

Rebased float-bar support

Original PR: #5262

[benmccann]

It looks like this is very close. There are two failing tests still

[kurkle]

Things to consider, I'm not saying they should be done though 😄

[benmccann]

@gwyneblaidd #6077 which implements the option not to skip borders has been merged now, so you shouldn't need any changes to element.rectangle.js anymore. Can you rebase the PR? Hopefully the other reviewers can take a look at this PR and we can merge it after that. It's very close. Thanks for sticking with it

I normally don't recommend squashing commits, but I find that if you have many commits then squashing them first makes rebasing easier, so you may want to consider in this case (git rebase HEAD~16, replace pick with s for all but the first commit, comment out all but the first commit message, git push -f)

[nagix]

Also, shouldn't we add docs in this PR?

[xaviRodri]

Good functionality!
Only one question: this [start, end] will only work for the y-axis, or will we be able to do the same in x-axis too?
Something like: {x: [start, end], y: value}
And a result like this: