Support URLs as input parameter

[buschtoens]

It would be great, if the {{link}} helper could support URLs that are recognizable by the router.

This would make {{link}} a more usable primitive in scenarios where a "serialized" URL has to be passed, e.g. as a callback query parameter.

{{! origin route }}
<Ui::Button
  @link={{link "signup" query=(hash callback=(get (link "checkout") "url"))}}
>
  Please sign up first to continue
</Ui::Button>

{{! "signup" target route }}
<Ui::Button
  @link={{link fromURL=callback}}
>
  Finish registration
</Ui::Button>