[prototype runtime] Avoid alias for methods defined in another module

[ksss]

define_method and define_singleton_method can take UnboundMethod in second argument.
In addition, it can be specified even for methods of a completely different module.

For example, erubi uses this technique.

https://github.com/jeremyevans/erubi/blob/4d24561e79e291208996892800a5cb9d11b8d2af/lib/erubi.rb#L23

rbs prototype runtime produces the following output for the current erubi.

$ rbs prototype runtime -r erubi Erubi
module Erubi
  alias self.h self.html_escape 

  ...snip...

However, the specified method does not exist.

Unknown method alias name: html_escape => h (::Erubi) (RBS::UnknownMethodAliasError)

    alias self.h self.html_escape
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

To avoid this problem, I suggest that in this case the output be as a method definition, not an alias.

[soutaro]

Thanks!