Allow trailing whitespace for complex messages

spec/message.abnf

@@ -5,7 +5,7 @@ simple-start      = simple-start-char / escaped-char / placeholder
 pattern           = *(text-char / escaped-char / placeholder)
 placeholder       = expression / markup
 
-complex-message   = *(declaration [s]) complex-body
+complex-message   = *(declaration [s]) complex-body [s]
 declaration       = input-declaration / local-declaration / reserved-statement
 complex-body      = quoted-pattern / matcher
 

spec/syntax.md

@@ -170,7 +170,7 @@ and consists of:
 2. a _complex body_
 
 ```abnf
-complex-message = *(declaration [s]) complex-body
+complex-message = *(declaration [s]) complex-body [s]
 ```
 
 ### Declarations

test/tests/syntax.json

@@ -409,6 +409,11 @@
           "type": "unsupported-statement"
         }
       ]
+    },
+    {
+      "src": "{{trailing whitespace}} \n",
+      "expCleanSrc": "trailing whitespace",
+      "exp": "trailing whitespace"
     }
   ]
 }