Remove `looseIdentical` implementation and instead use the ES2015 `Object.is` in its place.
They behave exactly the same way except for `+0`/`-0`.
`looseIdentical(+0, -0)` => `true`
`Object.is(+0, -0)` => `false`
Other than the difference noted above, this is not be a breaking change because:
1. `looseIdentical` is a private API
2. ES2015 is listed as a mandatory polyfill in the [browser support
guide](https://angular.io/guide/browser-support#mandatory-polyfills)
3. Also note that `Ivy` already uses `Object.is` in `bindingUpdated`.
PR Close#37191
toString() from DefaultIterableDiffer is only used in tests and should not
be part of the production code. toString() methods from differs add
~ 0.3KB (min+gzip) to the production bundle size.
toString() from DefaultKeyValueDiffer is only used in tests and should not
be part of the production code. toString() methods from differs add
~ 0.3KB (min+gzip) to the production bundle size.
