Add InstrumentationLibrary to Tracer

[ThomsonTan]

Fixes #567 and #694.

Changes

Add InstrumentationLibrary to SDK and return a new tracer for a different InstruementationLibrary.

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

Merging #693 (5b55dd1) into main (7909008) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #693      +/-   ##
==========================================
+ Coverage   94.79%   94.81%   +0.01%     
==========================================
  Files         212      214       +2     
  Lines        9707     9744      +37     
==========================================
+ Hits         9202     9239      +37     
  Misses        505      505              

Impacted Files	Coverage Δ
api/include/opentelemetry/trace/tracer.h	100.00% <ø> (ø)
sdk/test/trace/tracer_test.cc	100.00% <ø> (ø)
...k/instrumentationlibrary/instrumentation_library.h	100.00% <100.00%> (ø)
sdk/include/opentelemetry/sdk/trace/tracer.h	100.00% <100.00%> (ø)
sdk/src/trace/tracer.cc	79.31% <100.00%> (+2.38%)	⬆️
sdk/src/trace/tracer_context.cc	80.00% <100.00%> (ø)
sdk/src/trace/tracer_provider.cc	85.18% <100.00%> (+6.23%)	⬆️
...trumentationlibrary/instrumentationlibrary_test.cc	100.00% <100.00%> (ø)
sdk/test/trace/tracer_provider_test.cc	100.00% <100.00%> (ø)
... and 2 more

[jsuereth]

Change looks good assuming two things:

1. We create new Tracers for different libraries/versions (you have #694) for that.
2. We fill out InstrumentationLibrary in the OTLP exporter. Is there a bug open to track that work or do we need to open one?

[lalitb]

2. We fill out InstrumentationLibrary in the OTLP exporter. Is there a bug open to track that work or do we need to open one?

Created #695 for this.

[ThomsonTan]

Change looks good assuming two things:

1. We create new Tracers for different libraries/versions (you have Support multiple tracers in TracerProvider #694) for that.
2. We fill out InstrumentationLibrary in the OTLP exporter. Is there a bug open to track that work or do we need to open one?

Create new Tracer is also included in this PR (fixed #694). I'll work on filling out InstrumentationLibrary as a separate ticket (#695). We need populate this info to most exporters like OTLP, Zipkin, Jaeger, etc.

[seemk]

If GetTracer were to be used in an instrumentation to retrieve a tracer when creating spans, this potentially creates 3 allocations and deallocs on a hot path.

Would it make sense to avoid heap allocations here for the usual case when a tracer already exists?

I mean using GetTracer() every time could perhaps be considered bad use of the API as opposed to caching a tracer in the instrumentation, but I think it might be too easy too misuse the API and just default to GetTracer()

[ThomsonTan]

@seemk thanks. I think this is a valid concern. I updated the PR and delayed the heap allocation to the time when creating new Tracer is necessary.

[lalitb]

LGTM. Thanks for adding this feature.