Add link slot/render function support

[reinink]

As suggested by @sebastiandedeyne here, it would be great to add slot/render function support to the Inertia link. This provides a more advanced API for constructing Inertia links.

Vue example:

<inertia-link href="/logout" method="POST" v-slot="{ visit }">
  <button @click="visit">Log out<button>
</inertia-link>

React example:

<InertiaLink href="/logout" method="POST">
  {({ visit }) => <button onClick="visit">Log out</button>}
</InertiaLink>

This is similar to the v-slot API added to Vue Router in 3.1.0 (see here).