Show a closure’s type and actor isolation when performing cursor info on the braces or in keyword

[ahoppen]

When performing a cursor info on the braces or in keyword of a closure, it would be great if it showed the closure’s type and, more importantly, it’s actor isolation.

For example in the following test case, it should show something like @MainActor () -> Void

@MainActor func test() {
  // RUN: %sourcekitd-test -req=cursor -pos=%(line + 1):8 %s -- %s
  Task {
  }
}