Reconcile FeesAndCredits handling in price customization

Also adds a mechanism to ensure that fee extensions are included when custom
pricing logic adds a custom fee, and fixes up the domain restore flow to
properly use the restore price.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=142715136

javatests/google/registry/flows/domain/DomainApplicationUpdateFlowTest.java

@@ -679,7 +679,7 @@ public class DomainApplicationUpdateFlowTest
         newDomainApplication("non-free-update.tld").asBuilder().setRepoId("1-ROID").build());
     setEppInput(
         "domain_update_sunrise_fee.xml",
-        ImmutableMap.of("DOMAIN", "non-free-update.tld", "AMOUNT", "12"));
+        ImmutableMap.of("DOMAIN", "non-free-update.tld", "AMOUNT", "12.00"));
     clock.advanceOneMilli();
     thrown.expect(FeesMismatchException.class);
     runFlow();