Avoid redundant shutdown in LoggerProvider::drop when already shut down

[lalitb]

Changes

Prevents LoggerProvider::drop from calling shutdown if the provider has already been shut down.

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)

[codecov]

Codecov Report

Attention: Patch coverage is 87.85047% with 13 lines in your changes missing coverage. Please review.

Project coverage is 79.2%. Comparing base (20fd454) to head (637d3da).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-sdk/src/logs/log_emitter.rs	87.8%	13 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2195   +/-   ##
=====================================
  Coverage   79.2%   79.2%           
=====================================
  Files        121     121           
  Lines      20870   20964   +94     
=====================================
+ Hits       16532   16620   +88     
- Misses      4338    4344    +6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[cijothomas]

I have some comment left here:
https://github.com/open-telemetry/opentelemetry-rust/pull/2195/files#r1797268610

Please check if it makes sense. I am not I understand the reasoning fully why LoggerProvider is doing things differently than MeterProvider..