Closes#14954

I took a shot with the idea of thunkify every derived on the server to make them "work" in case of reassignment. As pointed out by@Rich-Harris this have some downside:

1. we re-execute possibly expensive deriveds on access
2. it's still more work than just accessing a variable

But I think regardless of the solution we will go with we will probably need functions in some way so this PR can be a good start.

I got 90% there in 10 minutes and then faced a big problem with destructured deriveds. Since we want every destructured identifier to be a function the only way i thought of is to do something like this.

letstuff=$state({foo:true,bar:[1,2,{baz:'baz'}]});let{ foo,bar:[a,b,{ baz}]}=$derived(stuff);

letstuff={foo:true,bar:[1,2,{baz:'baz'}]};let{foo:foo_1,bar:[a_1,b_1,{baz:baz_1}]}=stuff,foo=()=>foo_1,a=()=>a_1,b=()=>b_1,baz=()=>baz_1;

it's a bit more generated code but it works fine.

Again, this is a proposal, don't know if this the actual direction we want to go but even if it's not it could be a good base.

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