feat: Add ability to invalidate a custom identifier on goto()

[xxmichas]

Related issue: #10659

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[Rich-Harris]

preview: https://svelte-dev-git-preview-kit-13256-svelte.vercel.app/

this is an automated message

[eltigerchino]

I think this just stores the object reference and we're still mutating the same object later on.

[eltigerchino]

Can you add some tests as well to verify that it invalidates the correct load function when given a string, URL, or function?

[xxmichas]

@eltigerchino done, are they good?

[eltigerchino]

Thanks! I'd wait for the other maintainers to take a look at this too to see if this is the right API.