Handle GetAccessor and SetAccessor in isThisless (microsoft#27869)

Author: Andy Hanson

src/compiler/checker.ts

@@ -6364,7 +6364,9 @@ namespace ts {
                         case SyntaxKind.MethodDeclaration:
                         case SyntaxKind.MethodSignature:
                         case SyntaxKind.Constructor:
-                            return isThislessFunctionLikeDeclaration(<FunctionLikeDeclaration>declaration);
+                        case SyntaxKind.GetAccessor:
+                        case SyntaxKind.SetAccessor:
+                            return isThislessFunctionLikeDeclaration(<FunctionLikeDeclaration | AccessorDeclaration>declaration);
                     }
                 }
             }