[javascript] Separate @ from Identifier

pmd-javascript/etc/grammar/Ecmascript5.jj

@@ -281,8 +281,7 @@ TOKEN :
     |
         [
           "$",
-          "_",
-          "@"
+          "_"
         ]
     |
         <UNICODE_ESCAPE_SEQUENCE>
@@ -784,3 +783,13 @@ TOKEN :
 | < RSIGNEDSHIFTASSIGN: ">>=" > : DEFAULT
 | < RUNSIGNEDSHIFTASSIGN: ">>>=" > : DEFAULT
 }
+
+/*
+ * Decorators
+ * See https://github.com/tc39/proposal-decorators
+ */
+<DEFAULT,NOREGEXP,NOEOL>
+TOKEN :
+{
+    < AT: "@" > : DEFAULT
+}

pmd-javascript/src/test/resources/net/sourceforge/pmd/lang/ecmascript/cpd/testdata/decorator.txt

@@ -1,6 +1,7 @@
     [Image] or [Truncated image[            Bcol      Ecol
 L2
-    [@annotation]                           1         12
+    [@]                                     1         2
+    [annotation ]                           2         12
 L3
     [class]                                 1         6
     [MyClass]                               7         14