fix #29182, generate top level const fields lazily

pkg/dev_compiler/test/codegen_expected/node_modules.js

 'use strict';
 const dart_sdk = require('dart_sdk');
 const core = dart_sdk.core;
 const dart = dart_sdk.dart;
 const dartx = dart_sdk.dartx;
 const node_modules = Object.create(null);
 let B = () => (B = dart.constFn(node_modules.B$()))();
 let _B = () => (_B = dart.constFn(node_modules._B$()))();
 let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
 let VoidToString = () => (VoidToString = dart.constFn(dart.definiteFunctionType(core.String, [])))();
@@ skipping 11 matching lines @@
   dart.addTypeTests(_B);
   return _B;
 });
 node_modules._B = _B();
 node_modules.f = function() {
 };
 dart.fn(node_modules.f, VoidTodynamic());
 node_modules._f = function() {
 };
 dart.fn(node_modules._f, VoidTodynamic());
-node_modules.constant = "abc";
-node_modules.finalConstant = "abc";
 dart.defineLazy(node_modules, {
+  get constant() {
+    return "abc";
+  },
+  get finalConstant() {
+    return "abc";
+  },
   get lazy() {
     return dart.fn(() => {
       core.print('lazy');
       return "abc";
     }, VoidToString())();
-  }
-});
-node_modules.mutable = "abc";
-dart.defineLazy(node_modules, {
+  },
+  get mutable() {
+    return "abc";
+  },
+  set mutable(_) {},
   get lazyMutable() {
     return dart.fn(() => {
       core.print('lazyMutable');
       return "abc";
     }, VoidToString())();
   },
   set lazyMutable(_) {}
 });
 dart.trackLibraries("node_modules", {"node_modules.dart": node_modules}, null);
 // Exports:
 exports.node_modules = node_modules;