Do not display variables before they are initialized

[zardoy]

I found its useless to display variables before they are initialized. For example:

if (true) {
  | // a is displayed but shouldn't as it cant be used yet
}
const a = 5

However:

const b = () => {
    // here, a is okay to display, so check should not go outside of current function
}

const a = 5

Enabling it by default could surprise some users (it will be noticable completions change), also I'm not sure of any edge cases so lets make it optionable with setting (but with recommended flag)

[Ilanaya]

https://github.com/microsoft/TypeScript/blob/main/src/compiler/checker.ts#L3875