fix: router changes the URL prematurely

[si3nloong]

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[si3nloong]

Currently, the client-side navigation doesn't comply with the server-side navigation standard. We should change the URL path after the component or page is rendered.

This is a fix for issue #2870, but I think I need to include more test cases.

[Rich-Harris]

Thank you, but the current behaviour is intentional, and changing it would require a thorough discussion.

There's no universally accepted 'right' way to address this. This poll gives a slight edge to the behaviour in this PR...

...but the following thread gives some very convincing reasons why changing the URL at the start of the navigation makes more sense:

Personally I think delaying the change is worse UX — it robs the user of valuable feedback that their click was registered, and makes error recovery harder since they can't simply refresh the page if client-side navigation fails for some reason. I'm also persuaded by the argument that state should follow URL, not vice versa.

This position is supported by the behaviour of widely-used SPAs like YouTube and Instagram. Delaying the update until after a successful navigation would therefore violate the expectations that users have developed through using these sites.

[Rich-Harris]

Closing in favour of #3241 which has a simpler implementation, in case we were to decide to go ahead with this change