[SDK] Implement spec: MetricFilter

[IcySteam]

Fixes #2447

Changes

This PR implements the MetricFilter spec in opentelemetry-cpp.

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
  • MetricProducer::MetricProducer
  • MetricCollector::MetricCollector
  • MeterContext::AddMetricReader
  • MeterProvider::AddMetricReader

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: IcySteam / name: IcySteam (de7b80e)

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[marcalff]

@IcySteam

Thanks for the PR.

Please remember to sign the EasyCLA, so this PR can be processed.

[codecov]

Codecov Report

Attention: Patch coverage is 98.03922% with 1 line in your changes missing coverage. Please review.

Project coverage is 87.87%. Comparing base (6603c3a) to head (de7b80e).

Files with missing lines	Patch %	Lines
sdk/src/metrics/state/metric_collector.cc	97.06%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3235      +/-   ##
==========================================
+ Coverage   87.80%   87.87%   +0.08%     
==========================================
  Files         198      199       +1     
  Lines        6324     6362      +38     
==========================================
+ Hits         5552     5590      +38     
  Misses        772      772              

Files with missing lines	Coverage Δ
...e/opentelemetry/sdk/metrics/export/metric_filter.h	100.00% <100.00%> (ø)
...opentelemetry/sdk/metrics/export/metric_producer.h	100.00% <100.00%> (ø)
...opentelemetry/sdk/metrics/state/metric_collector.h	100.00% <ø> (ø)
sdk/src/metrics/meter_context.cc	76.06% <100.00%> (ø)
sdk/src/metrics/meter_provider.cc	86.85% <100.00%> (-0.33%)	⬇️
sdk/src/metrics/state/metric_collector.cc	91.53% <97.06%> (+4.43%)	⬆️

... and 1 file with indirect coverage changes

[lalitb]

@IcySteam Thanks for the PR. I believe you are working to get the CLA signed, as the PR can't be reviewed without that.

[IcySteam]

Thanks for the reminder @marcalff and @lalitb, CLA signing should be all done now.

[marcalff]

Thanks for the contribution, and for signing the CLA.

Before looking in more details at the code,
please see some preliminary comments below.

There should be no changes in third_party/opentelemetry-proto.

Please make sure to initialize and update git submodules in your branch.

Please check the "include-what-you-use" build in CI for warnings,
and fix the code to resolve them.

There should be no more warnings in the PR compared to the main branch.

More comments to follow.

[lalitb]

This was righty pointed out by @marcalff in community meeting - does this method need to return shared_ptr?

[lalitb]

@IcySteam It looks like you've now changed it to return a weak_ptr. Sorry I was not clear earlier, the question was—why does this method need to return anything at all?

[IcySteam]

@lalitb Returning the MetricCollector created by the MeterContext does seem like one of the only few ways to access the MetricCollector, as it is needed by MetricCollectorTest. Extending MetricCollector with a test class is also potentially viable, but that would require changing some of MetricCollector's private members to protected (or a friend class). What are your thoughts on writing proper tests in this case?