JET-172 Allow many parameters of a function literals to be declared without parentheses

grammar/src/expressions.grm

@@ -245,7 +245,7 @@ tupleLiteral
 // one can use "it" as a parameter name
 functionLiteral
   : "{" statements "}"
-  : "{" (type ".")? modifiers SimpleName "=>" statements "}"
+  : "{" (modifiers SimpleName){","} "=>" statements "}"
   : "{" (type ".")? "(" (modifiers SimpleName (":" type)?){","} ")" (":" type)? "=>" statements "}"
   ;