Make an assignment reactive without $: if it has reactive dependencies

Summary

It would be nice to have plain/concise assignment without redundant $: for variables that have reactive dependencies.

This is how we do now

let count = 1
$: doubled = count * 2

And this is how it can be

let count = 1
let doubled = count * 2

In case if we need one time doubled to be non reactive we could define it like

const doubled = count * 2