Set default method level to be public

Author: cindy-peng

gapic-generator-java/src/main/java/com/google/api/generator/gapic/model/Method.java

@@ -138,7 +138,7 @@ public static Builder builder() {
         .setStream(Stream.NONE)
         .setAutoPopulatedFields(new ArrayList<>())
         .setMethodSignatures(ImmutableList.of())
-        .setIsPublic(false)
+        .setIsPublic(true)
         .setIsBatching(false)
         .setIsDeprecated(false)
         .setOperationPollingMethod(false);