fix: correctly handle relative anchors when hash router is enabled

[eltigerchino]

fixes #13320

This PR enables relative hash links to be used with the hash router so that links such as #example get recognised as a link to the current page. We do this by assuming links that have a hash value starting with #/ links to a route while anything else is probably linking to an element with an id on the current page.

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🦋 Changeset detected

Latest commit: 0706244

The changes in this PR will be included in the next version bump.

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@sveltejs/kit	Patch

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[dummdidumm]

👍