[Java] Support camelCase enum type identifiers

The type identifier was previously used as-is (e.g. `carType`) in the
generated code for enums while generated enums always start with a
capital letter (`CarType`).

Author: pliard

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/java/JavaGenerator.java

@@ -3074,7 +3074,8 @@ private void generateEnumDecoder(
 
         if (fieldToken.isConstantEncoding())
         {
-            final String enumValueStr = fieldToken.encoding().constValue().toString();
+            final String enumValueStr = formatClassName(
+                fieldToken.encoding().constValue().toString());
 
             new Formatter(sb).format(
                 "\n" +