Avoid re-defining the entire Proxy type per-runtime

[kianenigma]

Just thinking out loud: re-writing all of this HIGHLY risky logic every time seems very dangerous to me. Ideally, we would have a base proxy builder that constructs the default NonTransfer, Any, Cancel etc, and we only extend it with the custom ones.

Originally posted by @kianenigma in https://github.com/paritytech/cumulus/pull/1346#discussion_r943154966

The answer can be a builder pattern or a macro.