Created by: ffoodd
Fixes #34292 (closed), fixes #34374 (closed), fixes #35616 (closed).
A few tries confirmed me that relying on border-width as in v4 doesn't imply any side effect, even when using the (deprecated) size attribute.
I don't see any reason to stick with height then, so ditching this to make our new hr closer to v4.
Contrary to what we said in #34574, we can keep the opacity feature this way. With my current proposal, customizing hr could be done using .text-* for color and .border-* for sizing. I'd stick to currentColor for color since it allows inheritance: relying on border-color would require us to define a value (as it was done in v4) but I think it's more valuable to inherit from text color, isn't it?
NB: the current migration guide mentions v5.2.0, which is not accurate, is it? Do we maintain a minor versions' migration guide anywhere?