[SDK] MeterProvider: do not warn in destructor after explicit Shutdown

[jaehyeong-cho]

Fixes #3511

Changes

Please provide a brief description of the changes here.

• Add test ensuring duplicate MeterProvider shutdown emits no log
• Modify MeterProvider to call context shutdown only once

It seems natural for MeterProvider to shut its context down from the destructor, and since MeterContext is a shared object, I think it is meaningful to warn about duplicate Shutdown calls.
However, I think it may not be a good experience that any user who calls the public MeterProvider::Shutdown API will always receive a warning log afterwards, because this isn't really a misuse case.
Therefore, with this PR, I would like to propose limiting MeterProvider to invoking the context shutdown at most once, so that no warning is emitted in the normal usage path.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.99%. Comparing base (16b1369) to head (25789e0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4085      +/-   ##
==========================================
- Coverage   82.01%   81.99%   -0.01%     
==========================================
  Files         385      385              
  Lines       16023    16025       +2     
==========================================
- Hits        13139    13138       -1     
- Misses       2884     2887       +3     

Files with missing lines	Coverage Δ
sdk/src/metrics/meter_provider.cc	80.77% <100.00%> (+0.77%)	⬆️

... and 2 files with indirect coverage changes

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[lalitb]

thanks.

[ThomsonTan]

Wondering why is this only fixed for ABI v2? The same issue applies to v1 ABI and the same fix could be applied there too.

[jaehyeong-cho]

Thanks for the review. I thought adding a member variable to a public class is ABI-breaking, so I tried to follow abi-version-policy.md and limited the change to ABI v2 only. If we saw this as a bug, I would try applying it to ABI v1 as well, but I thought it is not that serious.