Use ... in Display for Callable

Summary: Like [Python does](https://docs.python.org/3/library/typing.html#annotating-callables).

Reviewed By: IanChilds

Differential Revision: D63681890

fbshipit-source-id: a53a5f22beaee04631eff910e759d5244a7e59e5

Author: stepancheg

starlark/src/typing/callable.rs

@@ -83,7 +83,9 @@ impl Display for TyCallable {
             write!(f, "typing.Callable")?;
         } else {
             write!(f, "typing.Callable[")?;
-            if let Some(pos) = self.params().all_required_pos_only() {
+            if self.params().is_any() {
+                write!(f, "...")?;
+            } else if let Some(pos) = self.params().all_required_pos_only() {
                 write!(f, "[")?;
                 for (i, p) in pos.iter().enumerate() {
                     if i != 0 {