Return correct label for value type axis

[kurkle]

Fixes #5708

https://codepen.io/kurkle/pen/bOepaQ (updated to 4abdc59)

[benmccann]

@kurkle this change will have to be rebased

[kurkle]

Another way of fixing this, thoughts?

[simonbrunel]

@kurkle I think that's the solution I like the most. Since we are moving these methods in the base class, it may be the opportunity to make them explicitly private (prefixed by '_')? (IIRC, there was no "private" policy when I introduced these methods).

[kurkle]

@kurkle I think that's the solution I like the most. Since we are moving these methods in the base class, it may be the opportunity to make them explicitly private (prefixed by '_')? (IIRC, there was no "private" policy when I introduced these method).

done