Preload should be triggered on `goto(<self>)`

[mhkeller]

I'll make a proper reproduction repo this evening but for now scaffolding out the issue.

If you make a simple search form like this, preload should fire when you navigate using goto. It currently does not.

<svelte:head>
  <title>Search</title>
</svelte:head>

<h1>Search</h1>

<form class="search" method="GET">
  <input name="search" type="search" placeholder="" bind:value/>
  <input type="submit" />
</form>

<script>
import { goto } from 'sapper/runtime.js';

export default {
  data () {
    return {
      value: ''
    };
  },
  methods: {
    query (e) {
      e.preventDefault();
      const { value } = this.get();
      goto(`/search?search=${value}`);
    }
  },
  preload ({ query }) {
    console.log('this should appear on form submission. But it does not', query.search);
    // const results = await this.fetch(`search.json`);
  }
};
</script>

[Rich-Harris]

The reason for this is that it's ignoring everything after ? — goto(currentUrl) should be a noop (I would argue), but changing the query string would have to cause a full refresh (including tearing down the root component, in case it uses query in its oncreate hook...) in order to guarantee the correct behaviour.

Though I suppose we could preserve components that didn't have oncreate hooks, and just feed them new data... will have a think on this

[mrkishi]

I actually don't believe goto(currentUrl) should be a noop -- just like clicking a link to currentUrl isn't!

If it makes sense being a noop for a particular use-case, we can always manually implement it on top of goto. On the other hand, unless goto changes, we can't force it to trigger a page load.