Rename all testdata loading files to conform to a single naming scheme

The scheme is:
- loadBytes: returns a ByteSource of the data
- loadFile: returns a string using UTF8 encoding, optionally applying
  substitutions

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=177606406

javatests/google/registry/flows/contact/ContactTransferQueryFlowTest.java

@@ -50,7 +50,7 @@ public class ContactTransferQueryFlowTest
     eppLoader.replaceAll("JD1234-REP", contact.getRepoId());
     // Setup done; run the test.
     assertTransactionalFlow(false);
-    runFlowAssertResponse(readFile(expectedXmlFilename));
+    runFlowAssertResponse(loadFile(expectedXmlFilename));
     assertAboutContacts().that(reloadResourceByForeignKey(clock.nowUtc().minusDays(1)))
         .hasOneHistoryEntryEachOfTypes(HistoryEntry.Type.CONTACT_TRANSFER_REQUEST);
     assertNoBillingEvents();