[Progress] Styling feedback

[vladmoroz]

• In this current format, the Track part seems unnecessary for styling and fully duplicates Root
• data-progressing gives weird vibes. data-in-progress would be easier to remember as a more natural phrase
• When the value is at 0, the indicator doesn't have width: 0%. When using a transition on the width, this breaks the transition from 0.
• Having aria-label, aria-labelledby, aria-valuetext, getAriaLabel, getAriaValueText exposed as labelling props strikes me as a very different API style from most of the other components, which usually have separate parts for labelling. Perhaps worth reconsidering how to approach this.

[mj12albert]

When the value is at 0, the indicator doesn't have width: 0%. When using a transition on the width, this breaks the transition from 0

This one is just a bug 😐