Fix annotation parsing error with inner class signals

Author: NathanLovato

grammar.js

@@ -363,6 +363,7 @@ module.exports = grammar({
 
     signal_statement: ($) =>
       seq(
+        optional($.annotations),
         "signal",
         field("name", $.name),
         optional(field("parameters", $.parameters)),

test/corpus/source.txt

@@ -903,6 +903,27 @@ signal x(a, b: Type)
      (identifier)
      (type (identifier))))))
 
+=====================================
+Signal with annotation in inner class
+=====================================
+
+class State:
+	@warning_ignore("unused_signal")
+	signal exited
+
+---
+
+(source
+  (class_definition
+    name: (name)
+    body: (class_body
+      (signal_statement
+        (annotations
+          (annotation
+            (identifier)
+            arguments: (arguments (string))))
+        name: (name)))))
+
 =====================================
 Class Name
 =====================================