Add support for using Config, getProject(), getStack(), and isDryRun() from Policy Packs via upgraded dependency on @pulumi/pulumi v1.8.0 (requires v1.8.0 or later of the Pulumi SDK) (https://github.com/pulumi/pulumi-policy/pull/169).
Provide easier type checking for validateStack, along with isType and asType helper functions (https://github.com/pulumi/pulumi-policy/pull/173).

Example:
```
{
    validateStack: validateStackResourcesOfType(aws.s3.Bucket, (buckets, args, reportViolation) => {
        for (const bucket of buckets) {
            // ...
        }
    }),
}
```
validateTypedResource is now deprecated in favor of validateResourceOfType. validateTypedResource will be removed in an upcoming version. (https://github.com/pulumi/pulumi-policy/pull/173).
Attempting to access an unknown property value during previews from a stack validation callback now results in an advisory violation like what happens when doing the same from a resource validation callback (https://github.com/pulumi/pulumi-policy/pull/180).