Deep merge props from partial reloads

[lepikhinb]

Deep merge props on partial visits instead of simple concatenation, to preserve deeply nested props that are not present in the partial response. Array values will be replaced with new values.

Introduces required changes for inertiajs/inertia-laravel#620

Initial response:

{
  "user": {
    "id": 1,
    "name": "New user",
    "email": "boris@example.com"
  }
}

Partial request:

router.put(
  '/profile',
  {
    name: 'Boris Lepikhin'
  },
  {
    only: ['user.name'],
  }
)

Page props (auth.user.id preserved):

{
  "user": {
    "id": 1,
    "name": "New user",
    "email": "boris@example.com"
  }
}