feat: add $inspect.trace rune

[trueadm]

Closes #14265. This adds the $inspect.trace rune to Svelte which logs the reactive graph of the current reactive context. It must be placed in a block statement and requires a string passed as an argument which is the trace name.

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Latest commit: c3428fc

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pnpm add https://pkg.pr.new/svelte@14290

[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14290-svelte.vercel.app/

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[Ocean-OS]

Perhaps instead of having it compile to this:

$.user_effect(()=>{
return $.trace(()=>stuff, "name")
});

It could instead use a $.trace_effect (and $.trace_pre_effect) function that took an effect function and the trace name as arguments, and then:

1. The $.trace_effect function runs the effect to get the dependencies from the effect
2. The function destroys the effect
3. The function creates a new effect with the trace logging
   This new effect would not need to be run initially for dependency tracking, as the dependencies have already been found. Instead, the effect could just be added to the dependencies' reactions.

And then the code could instead compile to:

$.trace_effect(()=>stuff, "name");

I'm not sure how this will change in terms of performance (which shouldn't matter too much since its only running in dev mode), but it should result in less and simpler code.

[trueadm]

Perhaps instead of having it compile to this:

$.user_effect(()=>{
return $.trace(()=>stuff, "name")
});

This PR has compiled to that output for a while now. Worth checking it out again sometime :)

I'm not sure how this will change in terms of performance (which shouldn't matter too much since its only running in dev mode), but it should result in less and simpler code.

It wouldn't make anything simpler with the new design.

[trueadm]

@Rich-Harris Feel free to apply your local changes to this PR if that's easier.