Downgrade platform requirements

[aehlke]

note: I haven't tried macOS yet

[mlorenze]

Hi @aehlke!
Thank you for using our framework and contributing to it.
Related with downgrading to iOS15, there are issues with that when working with BarButtonStyle styles (is not showing the navBar).
So we won't update the framework with this PR.

[aehlke]

Hi @mlorenze your library works just fine on iOS 15 with the segmented style, which is the only way I use your lib. So I'd like to be able to continue to use the bar styles that do work on iOS 15. I noticed that your iOS 16 requirements were isolated to specific bar styles rather than various features scattered throughout, so I saw an opportunity to allow per style OS compatibility.

The bar styles that do work (segmented, at least) are fantastic: it's the native Apple UI which is a good default and common need. Please don't artificially prevent this bar style from being used when it works and looks like it'll continue to work on older versions given its simplicity in implementation compared with the custom UI styles.

As an aside, supporting not even 1 version back for a lib is a bit scary. I do that with my own apps sometimes, but am not always eager to shed the tens of % of users from one version back (not even a year out of date yet). This PR would at least allow falling back to native segmented control UI without forcing users to upgrade to an OS not even a year old yet.

Thanks