text: Title: Add explicit argument converter for `Any` that does no conversion
  Body: In Python's type system [Any](https://docs.python.org/3/library/typing.html#typing.Any) is used to indicate that any type is accepted. We should add an explicit argument convertor for `Any` that recognizes it but doesn't do any conversion. Because we don't do any conversion for unrecognized types, and  `Any` currently isn't recognized, this change wouldn't change much. It nevertheless has some benefits: 
  
  - `Any` will get its own type documentation pop-up in Libdoc HTML output explaining that all arguments are accepted without conversion.
  - It's becomes explicit that there's no conversion with `Any`. 
  - Behavior with `Any` won't change even if we later decide to handle unrecognized types differently than nowadays. See #4628 for related discussion.
  - It would have avoided issues reported in #4626. Those issues are now fixed, but adding `Any` converter would help removing the somewhat annoying workaround code that was added.
  