fix #11480, disallow delete operator on readonly property or index

signature

Author: HerringtonDarkholme

src/compiler/checker.ts

@@ -13550,6 +13550,9 @@ namespace ts {
 
         function checkDeleteExpression(node: DeleteExpression): Type {
             checkExpression(node.expression);
+            checkReferenceExpression(node.expression,
+                Diagnostics.The_operand_of_a_delete_operator_must_be_a_property_reference,
+                Diagnostics.The_operand_of_a_delete_operator_cannot_be_a_read_only_property);
             return booleanType;
         }
 

src/compiler/diagnosticMessages.json

@@ -1983,6 +1983,14 @@
         "category": "Error",
         "code": 2697
     },
+    "The operand of a delete operator must be a property reference": {
+        "category": "Error",
+        "code": 2698
+    },
+    "The operand of a delete operator cannot be a read-only property": {
+        "category": "Error",
+        "code": 2699
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",