Returns the package root of the current isolate, if any.
If the isolate is using a packageRoot or the isolate has not been
setup for package resolution, this getter returns null, otherwise it
returns the package config URI.
Returns the package root of the current isolate, if any.
If the isolate is using a packageRoot or the isolate has not been
setup for package resolution, this getter returns null, otherwise it
returns the package config URI.