Fix inconsistent rendering of shadow routes on client/server-side

[PH4NTOMiki]

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This PR fixes inconsistent URL handling for shadow routes on the client/server-side. and because of that it also
fixes #3777
fixes #3778

Tests

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Latest commit: 5a8ce9f

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[PH4NTOMiki]

@benmccann @bluwy please take a look, I'm pretty sure about the params part of the issue, I'll try to deal with the URLSearchParams tomorrow if they don't work with this.

[PH4NTOMiki]

I also fixed URLSearchParams issues, and I made URLSearchParams and the full url.href consistent in the shadow routes in both server and client routing. @Rich-Harris if I made mistake let me know, but I think this should be it.

[PH4NTOMiki]

should also fix #3777 and #3778

[benmccann]

@PH4NTOMiki if you put "fixes #3727 #3777 #3778" in the PR description it will only link one of the issues. you need to put the word fixes before each issue. I will edit the PR description to update

[Rich-Harris]

Thank you! This needs tests :)

Please only fix one issue per PR — I know it's tempting to do several simultaneously, but it slows things down (if this was two PRs we could add a test for the url.search addition and merge that immediately), makes reviews harder, and muddies the changelog and git history.

On the invalidation issue, the most straightforward logic would just be whether or not the pathname or query has changed. We need to have a proper think about what invalidation logic would look like if we had layout-shadowing endpoints, but this PR probably isn't the right place for it.

[PH4NTOMiki]

@Rich-Harris thanks Rich for reviewing, and thank you for the hard work on Svelte, I was planning to fix just #3727 but when i was reading the comments on that issue, many said the related/duplicate problem was with URLSearchParams and since they were kinda related I decided to fix them both in this PR.
So should I convert this PR just for the url.search and create a separate PR for invalidation logic?
or close this, and create 2 new?

Thankss

[Rich-Harris]

Whichever you prefer — converting this PR would be fine (we always squash commits before merging)

[PH4NTOMiki]

@Rich-Harris done

[timwis]

Thanks for this fix, @PH4NTOMiki! Looking forward to trying it out.

[PH4NTOMiki]

@Rich-Harris @benmccann can we merge this?

[PH4NTOMiki]

@bluwy can we merge this, cause it's a pretty serious bug.

[benmccann]

@PH4NTOMiki lint and the tests are failing. can you fix those issues?