Exceptions need to become localizable

[lizmat]

Inspired by rakudo/rakudo#2669

• No X::AdHoc (die) errors anymore
• No string attributes, except for names of methods / variables, etc.
• Enums for other specific reasons

[alabamenhu]

Hard agree. Then I can return in earnest to Intl::X which I haven't touched -- wait seriously four years? Yikes.

But as several pointed out in the rakudo thread -- .message really should just be a human readable form. Anything critical metadata should be provided through the error type (e.g. X::Method::NotFound or whatever it is) and its attributes (the method that wasn't found, and the type it was looked up on) to ease processing in a CATCH block.