[WIP] slog handler

[MrAlias]

This provides an overview of how to add the slog bridge. This PR as a whole is too large to ask review of. The plan to break this into smaller sections is as follows:

• Base stub structure of the following with TODO comments about implementation: Add skeleton of slog bridge #5292
  • Option
  • Handler
    • Handler.Handle
    • Handler.Enabled
    • Handler.WithAttrs
    • Handler.WithGroup
  • New
• Implement WithAttrs, WithGroup, and convertRecord while adding slogtest testing: Implement the slog Handler functionality #5314
• Add additional testing for multiple emits: Add multi-logged integration tests to otelslog #5329
• Add benchmark testing: Add benchmarks to otelslog #5330

Outstanding tasks

• Migrate from slogtest.TestHandler to slogtest.Run when support for Go 1.21 is dropped.
• Implement the Enabled method.
• Integrate the module version number into the Logger version using our build tooling and a Version function.
• Limit the returned size of objects returned to the kvBufferPool (integration testing will be needed): otelslog: Limit the size of kvBuffer returned to the pool #5334

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 14 lines in your changes are missing coverage. Please review.

Project coverage is 61.7%. Comparing base (6137d41) to head (20ce015).

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #5195     +/-   ##
=======================================
+ Coverage   61.2%   61.7%   +0.4%     
=======================================
  Files        185     187      +2     
  Lines      11207   11375    +168     
=======================================
+ Hits        6865    7019    +154     
- Misses      4142    4153     +11     
- Partials     200     203      +3     

Files	Coverage Δ
bridges/sloghandler/version.go	100.0% <100.0%> (ø)
bridges/sloghandler/handler.go	91.5% <91.5%> (ø)

[pellared]

Should we also set the SeverityText to the same values as https://cs.opensource.google/go/go/+/refs/tags/go1.22.1:src/log/slog/level.go;l=50-58?

Should it be configurable via an option?

If so then we would just need to make sure it does not cause any heap allocation.

TBH, I am not sure what is even the use case of having/using SeverityText. The specification does not say when/how it should be used.

[MrAlias]

Yeah, I think there is some confusion in general about this: open-telemetry/opentelemetry-specification#3933

[MrAlias]

Let's track with an issue.

[MrAlias]

These need to likely be the package/module name, not the bridge name: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/bridge-api.md#get-a-logger

The bridge name and version could be added as an attribute here. More investigation is required.

[pellared]

Maybe the bridge should simply accept log.Logger instead of log.LoggerProvider? Then the user would have full control what is the instrumentation scope.

[MrAlias]

Switched to accepting a logger.

[MrAlias]

Add the benchmarks to the PR description.