Platform.operatingSystemVersion on MacOS/iOS returns the version of the
kernel. It should instead returns system version.
This cl will try to use recently added "kern.osproductversion" to get
the system version. If it failed, try to read from "SystemVersion.plist".
Falls back to original kernal version if none of them succeed.
Bug: https://github.com/dart-lang/sdk/issues/41725
Change-Id: Ibbf78f10dc6d21b79d83d82fbcdacfd22ebc716d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/151165
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Zichang Guo <zichangguo@google.com>
Zichang Guo