Spacing in printed and generated signatures doesn't follow F# style guide

[dsyme]

The spacing we emit is inconsistent with the F# style guide https://docs.microsoft.com/en-us/dotnet/fsharp/style-guide/formatting#type-annotations

• Don't put a space before a colon, e.g. in val x: int.
• Do put a space between parameter name and type , e.g. val f: arg1: int -> arg2: int -> int

Exceptions for visual clarity are

• Put space after > for let v<'T> : int
• Put space when annotating the return type of a function/method, let f x : int = 1
• Put space after ) e.g. let (+) : int -> int -> int
• Put space for after a ` backtick, e.g. let ``a thing`` : int = 1

Fixing this unfortunately involves updating hundreds of test cases, but hey