[stdlib] ExpressibleByNilLiteral: allow ~Escapable conformers

Author: lorentey

stdlib/public/core/CompilerProtocols.swift

@@ -266,9 +266,9 @@ public protocol CaseIterable {
 /// `Optional` type conforms to `ExpressibleByNilLiteral`.
 /// `ExpressibleByNilLiteral` conformance for types that use `nil` for other
 /// purposes is discouraged.
-public protocol ExpressibleByNilLiteral: ~Copyable {
+public protocol ExpressibleByNilLiteral: ~Copyable, ~Escapable {
   /// Creates an instance initialized with `nil`.
-  init(nilLiteral: ())
+  init(nilLiteral: ()) -> dependsOn(immortal) Self
 }
 
 public protocol _ExpressibleByBuiltinIntegerLiteral {