feat: error when snippet shadow a prop

[paoloricciuti]

Svelte 5 rewrite

Closes #11603 ...i actually added a warning but i can change that to an error if it's preferred. The phrasing is also up to debate.

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[dummdidumm]

I think an error makes more sense because the prop will be completely ignored.

[paoloricciuti]

I think an error makes more sense because the prop will be completely ignored.

Yeah it make sense...i went for warn because the whole application might still works but error is better

[dummdidumm]

Thank you!