Enforce that all top-level value/function declarations have a type annotation.

Type annotations help to quickly understand what's expected in the code, and it will help the compiler give better error messages.

To also report let in declarations without a type annotation, additionally enable LetValueOrFunctionIsTypeAnnotated.

reported

a =
    1

not reported

b : number
b =
    let
        c =
            2
    in
    c