lib: add a diagnostic channel for observing AsyncContextFrame.set

[szegedi]

Adds an async_context_frame.set diagnostic channel for observing AsyncContextFrame.set.

This is helpful for functionality in extensions written in C++ that need to keep some derived native state from one or more AsyncLocalStorages in sync with changes in active frame. It is possible that such an extension needs to use the state when it can not enter V8 to obtain the data through AsyncLocalStorage JS API. A subscriber to this diagnostic channel can be used instead to eagerly keep the native state updated.

[Qard]

You should also add the channel to the diagnostics_channel docs here: https://github.com/nodejs/node/blob/main/doc/api/diagnostics_channel.md?plain=1#L1104

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.12%. Comparing base (535c2f7) to head (71104b3).
Report is 12 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #58229   +/-   ##
=======================================
  Coverage   90.12%   90.12%           
=======================================
  Files         629      629           
  Lines      186638   186638           
  Branches    36618    36622    +4     
=======================================
+ Hits       168202   168216   +14     
+ Misses      11222    11201   -21     
- Partials     7214     7221    +7     

Files with missing lines	Coverage Δ
lib/internal/async_context_frame.js	100.00% <100.00%> (ø)

... and 34 files with indirect coverage changes

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[Qard]

Might also be a good idea to have the tests validate that the frame can be used to look up the state for a given store. The store is the key so it should just be frame.get(store) to get the value.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/66711/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/66729/