Make ReasonPhrases compatible with codes as keys.

[james-pre]

Currently, we can use StatusCodes similar to a typescript enum like so:

console.log(StatusCodes.GONE); //411
console.log(StatusCodes[411]); //"Gone"

but this does not work with ReasonPhrases:

console.log(ReasonPhrases.GONE); //"Gone"
console.log(ReasonPhrases[411]); //undefined

We should be able to use ReasonPhrases[code]

[james-pre]

@prettymuchbryce Any updates on this?