fix #27631, get/set methods no longer shadow index operator

pkg/dev_compiler/test/codegen_expected/BenchmarkBase.js

 define(['dart_sdk'], function(dart_sdk) {
   'use strict';
   const core = dart_sdk.core;
   const dart = dart_sdk.dart;
   const dartx = dart_sdk.dartx;
   const BenchmarkBase$ = Object.create(null);
   let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
   BenchmarkBase$.Expect = class Expect extends core.Object {
     static equals(expected, actual) {
       if (!dart.equals(expected, actual)) {
         dart.throw(dart.str`Values not equal: ${expected} vs ${actual}`);
       }
     }
     static listEquals(expected, actual) {
       if (expected[dartx.length] != actual[dartx.length]) {
         dart.throw(dart.str`Lists have different lengths: ${expected[dartx.length]} vs ${actual[dartx.length]}`);
       }
       for (let i = 0; i < dart.notNull(actual[dartx.length]); i++) {
-        BenchmarkBase$.Expect.equals(expected[dartx.get](i), actual[dartx.get](i));
+        BenchmarkBase$.Expect.equals(expected[dartx._get](i), actual[dartx._get](i));
       }
     }
     fail(message) {
       dart.throw(message);
     }
   };
   dart.setSignature(BenchmarkBase$.Expect, {
     methods: () => ({fail: dart.definiteFunctionType(dart.dynamic, [dart.dynamic])}),
     statics: () => ({
       equals: dart.definiteFunctionType(dart.void, [dart.dynamic, dart.dynamic]),
@@ skipping 58 matching lines @@
       report: dart.definiteFunctionType(dart.void, [])
     }),
     statics: () => ({measureFor: dart.definiteFunctionType(core.double, [core.Function, core.int])}),
     names: ['measureFor']
   });
   // Exports:
   return {
     BenchmarkBase: BenchmarkBase$
   };
 });