feat(reflect): add @cpp1_rule_of_zero (#808)

* feat(reflect): add `@rule_of_zero`

* Prefix `cpp1_` to emphasize that this is a Cpp1 rule

This is about how to lower to Cpp1 code and let the Cpp1 defaults (the Cpp1 compiler-implemented type metafunction) take over

Cpp2 already embraces rule-of-zero in a different way/meaning, by having everything be opt-in all the time... if you write absolutely nothing, all you get is a default ctor and dtor

---------

Co-authored-by: Herb Sutter <herb.sutter@gmail.com>

Author: JohelEGP