Enumify PackageManager.PackageInfoFlags.Of

[jpobst]

We do not currently enumify PackageManager.PackageInfoFlags.Of (long) source because it is a long.

However, it seems to be a relatively used API so we should try to make it nicer.

As the values still fit in int, we are going to add an overload that takes our PackageInfoFlags enum.

If it overflows in the future, we will have to create a PackageInfoFlagsLong or similar enum an additionally add an overload for that.

We will perform this after previews for API-34 begins. If it already overflows int32 then we will determine a different route.