logtest: Add Recorder

[dmathieu]

This adds a Recorder into a new logtest log package, with the purpose of avoiding code repetition in each log bridge tests.

[dmathieu]

The links failure is expected, as the README currently points to a missing package.
Once the PR is merged, the package won't be missing anymore.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.9%. Comparing base (b9752eb) to head (a6d4db0).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #5134   +/-   ##
=====================================
  Coverage   83.8%   83.9%           
=====================================
  Files        254     255    +1     
  Lines      16539   16596   +57     
=====================================
+ Hits       13872   13927   +55     
- Misses      2374    2376    +2     
  Partials     293     293           

Files	Coverage Δ
log/logtest/recorder.go	100.0% <100.0%> (ø)

... and 1 file with indirect coverage changes

[pellared]

Bridges should not depend on the SDK.

I would rather prefer to have logtest with something like: https://github.com/open-telemetry/opentelemetry-go-contrib/blob/d15fe4f317e0376ff4a65a435b785a1c88e11b7c/bridges/otelslog/handler_test.go#L35-L76.

I think we could consider adding it to the go.opentelemetry.io/otel/log module (as go.opentelemetry.io/otel/log/logtest package) because one using the Bridge API would most likely would like to test the bridge implementation using this logtest package. Then we would not need to create test modules like https://github.com/open-telemetry/opentelemetry-go-contrib/blob/main/instrumentation/net/http/otelhttp/test/doc.go.

Related comment: open-telemetry/opentelemetry-go-contrib#5279 (comment)

[pellared]

🎉

[MrAlias]

Only non-nit is the comment about enabledFn.

[pellared]

@MadVikingGod, @dashpole, @XSAM, can you please review as it touches the API module?

[XSAM]

Looks good overall

[dashpole]

Optional suggestion