vdl/java: fix array length visibility of non-public classes

Change length of a fixed-length array from public static field
to class annotation, as through Java reflection you can see
all type information, but can't get the actual value.

Change-Id: Ie662a450165a2f92f60e7f8c7b23a4fe89312966
diff --git a/lib/vdl/codegen/java/file_array.go b/lib/vdl/codegen/java/file_array.go
index 4812cd1..e0ef7ab 100644
--- a/lib/vdl/codegen/java/file_array.go
+++ b/lib/vdl/codegen/java/file_array.go
@@ -23,11 +23,10 @@
  * type {{.Name}} {{.VdlTypeString}} {{.Doc}}
  **/
 @io.v.v23.vdl.GeneratedFromVdl(name = "{{.VdlTypeName}}")
+@io.v.v23.vdl.ArrayLength({{.Length}})
 {{ .AccessModifier }} final class {{.Name}} extends io.v.v23.vdl.VdlArray<{{.ElemType}}> {
     private static final long serialVersionUID = 1L;
 
-    public static final int LENGTH = {{.Length}};
-
     public static final io.v.v23.vdl.VdlType VDL_TYPE =
             io.v.v23.vdl.Types.getVdlTypeFromReflect({{.Name}}.class);