RFC: Simplify useParam behaviors

[nandorojo]

I'm considering removing initial, parse and stringify from useParam. I don't like that the behavior differs across platforms.

initial is certainly not needed, and is confusing realistically. I think the usage should instead be like this:

// before
const [item, setItem] = useParam('item', { initial: null })

// after
const [item = null, setItem] = useParam('item')

parse should either get removed, or should apply on both web and native equally. stringify was only added to match react-navigation's stack, but it feels unlikely to get used.

My hesitation with removing these is that I use them a lot. So I think this would be a sensible solution:

1. Rename initial to fallback, and apply it whenever the param is undefined. Currently, it uses a ref to track if it's the initial value, which feels hacky. It also might not work with concurrent mode (although, what will? lol). This approach also provides incorrect typesafety guarantees. If you set an initial value, then the TS types will not return undefined ever, even though they should.
2. Apply parse on both web and native.

[vinodsptharsha]

const [item, setItem] = useParam('items', 'fallbackValue')

I guess above pattern is followed by many libraries. Looks bit clean as well.