Issue Description:

In the following test case, SourceKit should provide cursor info for the literal 42, reporting its type as Double. Currently, it doesn’t return any information at all.

// RUN: %sourcekitd-test -req=cursor -pos=5:17 -print-raw-response %s -- %s

func foo() {
    let x = 1.2
    let y = x + 42
}

Original report:

Currently, clicking on a literal while holding the alt key in Xcode won't trigger a Quick Help pop-up. It may be useful for newcomers to be able to get the inferred type of a literal simply by invoking Quick Help.

In the Swift Forums' thread https://forums.swift.org/t/how-to-understand-the-int-double-conversion-in-swift/53063, a new user stumbled upon

3 + 0.14 // allowed

let three = 3
let rest = 0.14

3 + rest // allowed
0.14 + three // compile error
three + 0.14 // compile error

Quick Help triggered on the literal 3 at the first line or at the third-to-last line, would show

3: Double

A similar enhancement could be made to operator identifiers too, which would make easier for users to understand which overload has been chosen by the constraint solver.