fix(appender-tracing): always normalize event metadata when experimental_metadata_attributes is enabled

[dquirl-R1]

Fixes #3543
Design discussion issue (if applicable) #

Changes

Consistently applies NormalizeEvent if the experimental_metadata_attributes feature is active to ensure that the generated log records that are emitted forward the original log.target as the log event target instead of defaulting to "log".

The change impacts all extracted metadata, not just the target. It also applies to

• the severity, target and name used to check if self.logger.event_enabled (cf. Fix OTel Appender for tracing from suppressing other layers #2668, feat: Allow event name to be provided to IsEnabled check in Logger #2756)
• the severity number set on the log record itself
• the severity text set on the log record itself, which is derived from the event metadata level

It does not affect the behaviour of EnvFilter, because of the interaction between tracing-log normalizing through AsTrace (a different normalization) before calling enabled on the dispatcher in dispatch_record and the way EnvFilter caches FilterState and doesn't use event_enabled (see also #3543 (comment)).

Note that this reverts #2799 as the optimization is incompatible with applying normalization before setting the target.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[linux-foundation-easycla]

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[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.0%. Comparing base (7b24be9) to head (ea66c3a).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-appender-tracing/src/layer.rs	66.6%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #3582     +/-   ##
=======================================
- Coverage   83.0%   83.0%   -0.1%     
=======================================
  Files        130     130             
  Lines      28064   28063      -1     
=======================================
- Hits       23321   23320      -1     
  Misses      4743    4743             

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[github-actions]

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