Slider

A range control with a name, which is harder than it sounds.

The thumb is the focusable element and Bits gives it the role, the value and
the arrow keys — but not a name.

`<label for>` does not work here: a `<span role="slider">` is not a labelable
element, so the connection has to go through `aria-labelledby` to the field's
label. Without it the slider has no accessible name at all. The browser-based
accessibility gate caught exactly this, while 146 jsdom tests were green —
because they never asked for the name.