Update parser early return type in ESNEXT (#3742)

This patch updates the early return types in the parser to SyntaxError instead of ReferenceError
in ESNEXT

This patch also includes a lot of tests for LeftHandSideExpression validation when using the = operator

JerryScript-DCO-1.0-Signed-off-by: Adam Szilagyi aszilagy@inf.u-szeged.hu

jerry-core/parser/js/js-parser-util.c

@@ -968,6 +968,18 @@ parser_error_to_string (parser_error_t error) /**< error code */
     {
       return "Duplicate __proto__ fields are not allowed in object literals.";
     }
+    case PARSER_ERR_INVALID_LHS_ASSIGNMENT:
+    {
+      return "Invalid left-hand side in assignment.";
+    }
+    case PARSER_ERR_INVALID_LHS_POSTFIX_OP:
+    {
+      return "Invalid left-hand side expression in postfix operation.";
+    }
+    case PARSER_ERR_INVALID_LHS_FOR_LOOP:
+    {
+      return "Invalid left-hand-side in for-loop.";
+    }
 #endif /* ENABLED (JERRY_ESNEXT) */
     case PARSER_ERR_DELETE_IDENT_NOT_ALLOWED:
     {