In Python's type system 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 Support registering default argument converter #4628 for related discussion.
• It would have avoided issues reported in Inconsistent argument conversion when using None as default value with Python 3.11 and earlier #4626. Those issues are now fixed, but adding Any converter would help removing the somewhat annoying workaround code that was added.