[Java] Reduce allocation when displaying var data in Java codecs.

Author: mjpt777

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

@@ -3262,14 +3262,14 @@ private void appendDecoderDisplay(
             append(sb, indent, "builder.append(\"" + varDataName + Separators.KEY_VALUE + "\");");
             if (null == characterEncoding)
             {
-                append(sb, indent, "builder.append(" + varDataName + "Length() + \" bytes of raw data\");");
+                append(sb, indent, "builder.append(" + varDataName + "Length()).append(\" bytes of raw data\");");
                 append(sb, indent,
                     "parentMessage.limit(parentMessage.limit() + " + varDataName + "HeaderLength() + " +
                     varDataName + "Length());");
             }
             else
             {
-                append(sb, indent, "builder.append('\\'' + " + varDataName + "() + '\\'');");
+                append(sb, indent, "builder.append('\\'').append(" + varDataName + "()).append('\\'');");
             }
 
             lengthBeforeLastGeneratedSeparator = sb.length();