support empty param in lg template (#2855)

libraries/Microsoft.Bot.Builder.LanguageGeneration/LGFileParser.g4

@@ -40,7 +40,7 @@ templateName
     ;
 
 parameters
-    : OPEN_PARENTHESIS? IDENTIFIER (COMMA IDENTIFIER)* CLOSE_PARENTHESIS?
+    : OPEN_PARENTHESIS (IDENTIFIER (COMMA IDENTIFIER)*)? CLOSE_PARENTHESIS
     ;
 
 templateBody

libraries/Microsoft.Bot.Builder.LanguageGeneration/StaticChecker.cs

@@ -209,16 +209,6 @@ namespace Microsoft.Bot.Builder.LanguageGeneration
                     {
                         result.AddRange(Visit(context.templateBody()));
                     }
-
-                    var parameters = context.templateNameLine().parameters();
-                    if (parameters != null)
-                    {
-                        if (parameters.CLOSE_PARENTHESIS() == null
-                               || parameters.OPEN_PARENTHESIS() == null)
-                        {
-                            result.Add(BuildLGDiagnostic($"parameters: {parameters.GetText()} format error", context: context.templateNameLine()));
-                        }
-                    }
                 }
 
                 return result;

tests/Microsoft.Bot.Builder.LanguageGeneration.Tests/Examples/3.lg

@@ -1,13 +1,13 @@
 > Welcome Phrase template
 > LG runtime will pick a text value from the one-of collection list at random.
-# wPhrase
+# wPhrase  ()
 - Hi
 - Hello
 - Hiya
  
 > Using a template in another template
 > Sometimes the bot will say 'Hi' and other times it will say 'Hi :)'
-# welcome-user
+# welcome-user()
 - [wPhrase]
 - [wPhrase] :)