Object rest does not preserve enumerable Symbol keys

[Jessidhia]

Checked with the improved __rest helper from this PR, but also applies to master.

The CopyDataProperties operation that is used to define object rest uses the [[OwnPropertyKeys]] operation, which does return Symbols (https://tc39.github.io/ecma262/#sec-ordinaryownpropertykeys).

for .. in, however, skips over Symbol keys; a potential fix it so do a second copy loop with the result of Object.getOwnPropertySymbols if available.

Screenshot of a Chrome REPL session comparing __rest's behavior with Object.assign, which is supposed to have (almost) the same copying behavior:

[sandersn]

The fix is available now. I folded it into #12248