RFC for Function and Method Stubbing (rust-lang#1723)

* Start drafting RFC.

* Update example.

* Flesh out more sections.

* Update RFC with some of Adrian's feedback.

* Some more bullets on function contracts.

* Some updates; add section on stub sets.

* Add implementation alternatives.

* Add information about accessing private fields; more updates.

* Add Vec example.

* Tweaks.

* Add proof-of-concept link.

* Update links.

* More link work.

* Some work on motivation.

* Clean up mocking randomization section.

* Remove old material.

* Update rfc/src/rfcs/0002-function-stubbing.md

Co-authored-by: Celina G. Val <[email protected]>

* Serde example.

* Add text to Firecracker example.

* Implement Celina's suggestions.

* Update design section.

* Clarifications about design.

* Remove section on accessing private fields.

* Update section on stub sets to use macro.

* Implement Adrian's suggestions.

* Tweaks.

* More tweaks.

* Standardize titles.

* Integrate feedback.

* Do not use string literals in attributes.

* A few language tweaks.

* Change kani::stub_by to kani::stub.

* Move Firecracker example to appendix.

* Update rfc/src/rfcs/0002-function-stubbing.md

Co-authored-by: Zyad Hassan <[email protected]>

* Integrate more of zhassan-aws's feedback.

* Tweak capitalization.

* Update stub set syntax.

Co-authored-by: Celina G. Val <[email protected]>
Co-authored-by: Zyad Hassan <[email protected]>

Author: 3 people