fix: access mapInstance outside of Map component

[jinn2u]

hi, first of all I'm big fan of you.
i have little idea in this library

AS-IS
to access map instance, we can use useMapContext
but because of Provider is inside of Map component, map instance is accessible only from child components with the map component as a parent.

const InnerMap = () => {
    const map = useMapContext()
    return (
        ...
    )
}
const NaverMap = () => {
    return (
    <Map
      <InnerMap />
    </Map>
    )
}

TO-BE
how about change usage of useMapContext like this?

index.tsx
<MapContextProvider>
    <App />
</MapContextProvider>

App.tsx

function App() {
  const map = useMapContext();
  return (
    <Map />
  );
}

i'll make pr if you ok.

[josworks27]

I agree with your idea. And I want you to contribute to this project.

Thank you.