YaruBackButton alignment behavior is inconsistent

[d-loose]

Depending on whether its style is round or not, the button is wrapped in a Center() widget (see #531). Consequently, ubuntu/app-center#1622 lead to a misalignment in the App Center's search page:

Of course, this can be fixed very easily, but I suppose it's worth making the behavior consistent in yaru 🙂

[spydon]

Ideally, doesn't this look better?

[Feichtmeier]

It should be in the leading spot of the appbar, when the page is paned, IMO, just like in the yaru.dart example :) or in the firmware updater / settings app / musicpod / etc
Not to distract from the actual issue, but the back button placement was really questionable from the beginning, IMHO 🙏