Use a correct Object.entries polyfill

[RyanCavanaugh]

Fixes #40243

The prior polyfill initialized the array slots with keys.length, then used push, creating a sparse array:

> console.log(_entries({ a: 1, b: "", c: false, 4: "d" }));

[ <4 empty items>,
  [ '4', 'd' ],
  [ 'a', 1 ],
  [ 'b', '' ],
  [ 'c', false ] ]

[DanielRosenwasser]

Please make sure this gets ported to tslib as well if you merge it

[DanielRosenwasser]

😂 sorry, I totally forgot about that. That must've been painful without a good error message.