Overload display fixes

[RblSb]

• typerDisplay change inverts signature overloads list, currently it's displayed incorrectly in IDE
• typer change fixes foo(S| completion by re-raising Unknown_ident error, so there is still Some/None reported fields in completion while typing names
• callUnification change fixes foo(<completion>) case, when foo signature has second argument like (a:Option<Bool>, cb:() -> Void) and foo(<inserted null display value>) gets Not_enough_arguments for second cb argument. Now completion items for first overload is preserved, since extract_delayed_display should be called before loop candidates, that processes second Int overload, also gets Not_enough_arguments error and incorrectly overwrites ctx.g.delayed_display with Int overload)