* Add support for the SupportedOSPlatformVersion MSBuild property, and write
it to the Info.plist for the corresponding minimum OS version.
* If there are any minimum OS version in the Info.plist, we'll now show an
error if it doesn't match SupportedOSPlatformVersion.
This unfortunately means that if there's any minimum OS version in any
Info.plist, then that will most likely have to be moved to the
SupportedOSPlatformVersion property (or removed entirely if that's the right
choice), since it's unlikely to match the default value for
SupportedOSPlatformVersion. However, this was deemed to be the best option for
the future (it's a one-time pain during migration).
Also add new tests, update existing tests, and update the templates.
Fixes https://github.com/xamarin/xamarin-macios/issues/12336.
24ea02759f