Prevent removeChild exception

[Swizz]

This fix the

 DOMException: Failed to execute 'removeChild' on 'Node': The node to be removed is not a child of this node.

exception occuring when changing route using Sapper.

This occur because of the deletetion of the node in the DOM before of the destroy lifecycle being called.

fix #1

[Swizz]

I dont know the need behind the use of destroy.

But I would recommand to use of the following, instead

function fragment(node) {
  node.parentElement.appendChild(document.adoptNode(node).content);
}

That will produce a more clean domtree close to what we wanted at start. sveltejs/svelte#2080

Orginal behavior :

Proposed behavior :

The node adoption make sense because the template tag will not be reuse in the context. It the one time use. And given the slot use, it should not be use in another context.

I will personnaly strongly stand in favor of adoptNode.

[Swizz]

Well. I found out the why of the destroy lifecycle need. But it is also the orginal reason of the bug.
Even the original PR will solve nothing. I will continue to work on this.

I focused my self on the Sapper routing, but conditional rendering and loop are involed too.

edit:
To provide explanation. When a fragment is added as node child its content is spread as children, but it seem we are not able to use the fragment content to remove these childs from the DOM.

From : https://developer.mozilla.org/en-US/docs/Web/API/DocumentFragment#Usage_notes

Doing this moves the fragment's nodes into the DOM, leaving behind an empty DocumentFragment. Because all of the nodes are inserted into the document at once, only one reflow and render is triggered instead of potentially one for each node inserted if they were inserted separately.

That's why we can't remove child from an used fragment.

[Swizz]

Here is the workaround I found.
I let you some comments @qutran, to open the discussion about it.

[Swizz]

Following a weird behavior of Sapper. This feature should be needed too.

Because of SSR, I would love to not necessarly use a template element as slot node.
This change mimic the fragment behavior for non template nodes.