[docs/rfc] Add component interface guidelines

[jmacd]

Description

Specifies the mechanics of our approach to safe interface evolution.

See #14523
See #14525
See #13902

Testing

This pattern was "tested" in #13241 as I prototyped a rate-limiter extension.

Documentation

✅

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.34%. Comparing base (c62f512) to head (4c1c218).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14532   +/-   ##
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  Coverage   90.34%   90.34%           
=======================================
  Files         699      699           
  Lines       53748    53748           
=======================================
  Hits        48559    48559           
  Misses       4044     4044           
  Partials     1145     1145           

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[evan-bradley]

Thanks for writing this, I wish I had this document when starting to work on the repo.

[evan-bradley]

Amended the title just to make it a bit clearer this is an RFC.

Also @jmacd could you add a short blurb linking to this document in CONTRIBUTING.md? I think it's a great contributor resource.

[mx-psi]

@jmacd Can you make sure you have followed the 'announcement' requirements for RFCs?

[jmacd]

As per #14532 (comment) we should hold off I will announce this as described.

[jmacd]

Fully announced, by now :-)

[mx-psi]

@jmacd Can you fix the Markdown issues? If CI is fixed, I will merge this on Friday morning unless there are blocking comments by then

[mx-psi]

@jmacd I am ready to merge this whenever you fix the checks job