Simplify progress bar theme management

[jecisc]

The theme management of the progress bar is a little messy because it gives a progress bar parameter that is never used. And some methods have "style" in the name but they should return colors.

Here is a pass to simplify this. I'll then do a next step to ensure that Spec is using those methods to theme the progress bars in Spec because this is not the case currently

[MarcusDenker]

again a segmenation fault on loading, but another package (was before when loading spec, now on newtools). I opened https://github.com/pharo-project/pharo/issues/17286