Use Multimap bindings to construct BigQuery schema map

This refactoring allows the schemas to live in the same package they
are used, rather than all having to be inside the bigquery package.
This is a follow-up to []
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=120551011

javatests/com/google/domain/registry/export/UpdateSnapshotViewActionTest.java

@@ -113,6 +113,10 @@ public class UpdateSnapshotViewActionTest {
   public void testSuccess_doPost() throws Exception {
     action.run();
 
+    // Check that the BigQuery factory was called in such a way that the dataset would be created
+    // if it didn't already exist.
+    verify(bigqueryFactory).create("Project-Id", "latest_snapshot");
+
     // Check that we updated the view.
     ArgumentCaptor<Table> tableArg = ArgumentCaptor.forClass(Table.class);
     verify(bigqueryTables).update(