Rename PricingEngine to PremiumPricingEngine

This properly reflects the fact that other, separate things will now
be responsible both for EAP and for per-TLD custom pricing.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=124558165

javatests/google/registry/testing/DatastoreHelper.java

@@ -235,7 +235,7 @@ public class DatastoreHelper {
       .setServerStatusChangeBillingCost(Money.of(USD, 19))
       // Always set a default premium list. Tests that don't want it can delete it.
       .setPremiumList(persistPremiumList(tld, DEFAULT_PREMIUM_LIST_CONTENTS.get()))
-      .setPricingEngineClass(StaticPremiumListPricingEngine.class)
+      .setPremiumPricingEngineClass(StaticPremiumListPricingEngine.class)
       .build();
   }