add onPress props to AppBar.BackAction

Author: idl-tdeconinck

src/Paper__Appbar.re

@@ -59,6 +59,7 @@ module Header = {
 
 module BackAction = {
   [@bs.module "react-native-paper"] [@bs.scope "Appbar"] [@react.component]
-  external make: (~accessibilityLabel: string=?) => React.element =
+  external make:
+    (~accessibilityLabel: string=?, ~onPress: 'a => unit) => React.element =
     "BackAction";
 };