[API/SDK] Provider cleanup

[marcalff]

Fixes #2506

Changes

Please provide a brief description of the changes here.

• Removed methods related to Flush() and Close() from the API class opentelemetry::trace::Tracer, starting with ABI version 2.
  • These methods are not intended for the API, and got exposed as an oversight
  • These methods belong to the SDK instead
• Changed all XXXProviderFactory::Create() methods to return an SDK object instead of an API object.
  • Returning an SDK object is necessary for the application code to perform a proper initialisation, and proper shutdown of the SDK
  • In particular, returning an SDK object is required for the caller to invoke Flush() and Shutdown().
• Removed static_cast<SDK*>(API object) from examples, and use cleaner code, to initialize SDK providers.
• Because the SDK change is breaking, provided a compile flag and a migration path. This allows applications:
  • To upgrade to the latest opentelemetry-cpp immediately, without code changes
  • To plan for code adjustments at a later date.

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

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

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 30.00000% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 87.68%. Comparing base (497eaf4) to head (79595f5). Report is 72 commits behind head on main.

Additional details and impacted files

[](https://app.codecov.io/gh/open-telemetry/opentelemetry-cpp/pull/2664?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry) ```diff @@ Coverage Diff @@ ## main #2664 +/- ## ========================================== + Coverage 87.12% 87.68% +0.56% ========================================== Files 200 190 -10 Lines 6109 5851 -258 ========================================== - Hits 5322 5130 -192 + Misses 787 721 -66 ``` | [Files](https://app.codecov.io/gh/open-telemetry/opentelemetry-cpp/pull/2664?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry) | Coverage Δ | | |---|---|---| | [api/include/opentelemetry/trace/noop.h](https://app.codecov.io/gh/open-telemetry/opentelemetry-cpp/pull/2664?src=pr&el=tree&filepath=api%2Finclude%2Fopentelemetry%2Ftrace%2Fnoop.h&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry#diff-YXBpL2luY2x1ZGUvb3BlbnRlbGVtZXRyeS90cmFjZS9ub29wLmg=) | `93.34% <ø> (ø)` | | | [api/include/opentelemetry/trace/tracer.h](https://app.codecov.io/gh/open-telemetry/opentelemetry-cpp/pull/2664?src=pr&el=tree&filepath=api%2Finclude%2Fopentelemetry%2Ftrace%2Ftracer.h&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry#diff-YXBpL2luY2x1ZGUvb3BlbnRlbGVtZXRyeS90cmFjZS90cmFjZXIuaA==) | `100.00% <ø> (ø)` | | | [sdk/include/opentelemetry/sdk/trace/tracer.h](https://app.codecov.io/gh/open-telemetry/opentelemetry-cpp/pull/2664?src=pr&el=tree&filepath=sdk%2Finclude%2Fopentelemetry%2Fsdk%2Ftrace%2Ftracer.h&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry#diff-c2RrL2luY2x1ZGUvb3BlbnRlbGVtZXRyeS9zZGsvdHJhY2UvdHJhY2VyLmg=) | `100.00% <ø> (ø)` | | | [sdk/src/logs/event\_logger\_provider\_factory.cc](https://app.codecov.io/gh/open-telemetry/opentelemetry-cpp/pull/2664?src=pr&el=tree&filepath=sdk%2Fsrc%2Flogs%2Fevent_logger_provider_factory.cc&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry#diff-c2RrL3NyYy9sb2dzL2V2ZW50X2xvZ2dlcl9wcm92aWRlcl9mYWN0b3J5LmNj) | `100.00% <ø> (ø)` | | | [sdk/src/trace/tracer\_provider\_factory.cc](https://app.codecov.io/gh/open-telemetry/opentelemetry-cpp/pull/2664?src=pr&el=tree&filepath=sdk%2Fsrc%2Ftrace%2Ftracer_provider_factory.cc&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry#diff-c2RrL3NyYy90cmFjZS90cmFjZXJfcHJvdmlkZXJfZmFjdG9yeS5jYw==) | `44.83% <30.00%> (+0.39%)` | :arrow_up: | ... and [70 files with indirect coverage changes](https://app.codecov.io/gh/open-telemetry/opentelemetry-cpp/pull/2664/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=open-telemetry)

[lalitb]

Good catch :)

[marcalff]

Waiting for the build to finish to make sure DLL links, then this will be ready for review.

[marcalff]

Add help-wanted label:

The windows DLL build fails with undefined symbols, and I can not figure out why (I don't have windows locally to investigate).