let hash changes be handled by the router

[lukasIO]

Allow router to handle hash only changes in order to make browser (back) navigation to hash routes work.
Fixes #821

[benmccann]

Hmm. I'm not quite sure I understand the issue. If I go to https://kit.svelte.dev/docs, click a section in the lefthand side menu, click the github link at the top of the page, then click back, it still goes to the section I clicked on and has # in the URL

It's also interesting that it was explicitly disallowed before. I'd kind of want to know the reason for that. It might be helpful to find the change in Sapper that introduced that line

[lukasIO]

The issue only manifests itself if the second link (after clicking on the hash link) is also a route within the SvelteKit project. You can check the reproduction repository in #821 to confirm or alternatively run the tests that I added in 31e0e87 on the current implementation to confirm.

[benmccann]

I still need to review this, but in the meantime can you add a changeset by running pnpx changeset?

[lukasIO]

maybe the right way to go about this, would be to choose to history.replaceState for hash only navigation? Not entirely sure what the desired behaviour should be.

[benmccann]

Thanks for your patience on this PR. I finally got a chance to test it and I think it looks good as is. Can you rebase it? Then I think we can merge

[lukasIO]

thanks @benmccann for reviewing and rebasing!