On Android versions prior to Oreo, the instant app icon isn't shown
anywhere, so some Unity apps are being uploaded without one. However,
on Oreo and later devices the icon is used, so display a warning when
performing a publish build without an icon.
Also rearrange some of the build prerequisite checks for easier reuse.
Also display publish build errors prior to showing the "Save" dialog.
On Android versions prior to Oreo, the instant app icon isn't shown anywhere, so some Unity apps are being uploaded without one. However, on Oreo and later devices the icon is used, so display a warning when performing a publish build without an icon.
Also rearrange some of the build prerequisite checks for easier reuse. Also display publish build errors prior to showing the "Save" dialog.