Consistent behavior change flag names + deprecation warnings

[jtcohen6]

resolves #10062

Problem

Behavior change flags have inconsistent naming + use of the deprecations module for firing warnings.

Solution

Rename flags + use deprecations module, as described here (internal notion)

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.14%. Comparing base (1a9fb61) to head (e620796).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10063      +/-   ##
==========================================
- Coverage   88.15%   88.14%   -0.01%     
==========================================
  Files         181      181              
  Lines       22683    22700      +17     
==========================================
+ Hits        19996    20009      +13     
- Misses       2687     2691       +4     

Flag	Coverage Δ
integration	85.46% <100.00%> (-0.01%)	⬇️
unit	62.34% <72.97%> (+<0.01%)	⬆️

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[MichelleArk]

I've made some non-functional changes -- added documentation, updated changelog entry, reformatted the generated protos, and made the world's tiniest refactor.

The actual core changes here look great, thank you!