Function completion should leverage trailing closure syntax #854
Description
Given func foo(a: Int, b: () -> ()) {}, the completion for foo is foo(a: Int, b: () -> ()) with snippets on the types. It's more swifty to use the trailing closure syntax, so it would be nice for this to be foo(a: Int) {}, or some variant inside the closure.
Bonus points if the trailing closure syntax is avoided if the expression is inside of an if / while statement since that generates a warning that the curly braces are confusing.
