Use the location passed in through the custom router if it exists

[jasong689]

If a custom router is passed to the Provider we should use that to determine any query params in the URL (for things like host). This will work better for technologies like Next that may have a SSR component and have a custom router. This would allow you to do something like the following for Next:

const router = useRouter()

<GadgetProvider 
    type={AppType.Embedded}
    shopifyApiKey={process.env.NEXT_PUBLIC_SHOPIFY_API_KEY!} 
    api={api}
    router={{
        location: router.asPath,
        history: router
    }}>
...
</GadgetProvider>