Fixes #1837. Add additional unnecessary null-ckeck warnings (#1842)

Author: sgrekhov

LanguageFeatures/Patterns/null_check_A02_t01.dart

@@ -23,6 +23,9 @@ String test1(int? x) {
 // [cfe] The null-check pattern will have no effect because the matched type isn't nullable.
       return "match-1";
     case int v2?:
+//             ^
+// [analyzer] STATIC_WARNING.UNNECESSARY_NULL_CHECK_PATTERN
+// [cfe] The null-check pattern will have no effect because the matched type isn't nullable.
       return "match-2";
     default:
       return "no match";
@@ -37,6 +40,9 @@ String test2(int? x) {
     return "match-2";
   }
   if (x case int v2?) {
+//                 ^
+// [analyzer] STATIC_WARNING.UNNECESSARY_NULL_CHECK_PATTERN
+// [cfe] The null-check pattern will have no effect because the matched type isn't nullable.
     return "match-2";
   }
   return "no match";
@@ -49,6 +55,9 @@ String test3(int? x) =>
 // [analyzer] STATIC_WARNING.UNNECESSARY_NULL_CHECK_PATTERN
 // [cfe] The null-check pattern will have no effect because the matched type isn't nullable.
     int v2? => "match-2",
+//        ^
+// [analyzer] STATIC_WARNING.UNNECESSARY_NULL_CHECK_PATTERN
+// [cfe] The null-check pattern will have no effect because the matched type isn't nullable.
     _ => "no match"
   };