Rename OTEL_CPP_GET_ATTR macro, and define it using fully qualified attr function.

[lalitb]

Fixes #1139

Changes

• Renamed OTEL_CPP_GET_ATTR macros defined for resource and trace into two different sem-ver macros - OTEL_GET_TRACE_ATTR (for trace) and OTEL_GET_RESOURCE_ATTR (for resource). This will avoid name overwriting if both are used in the same application.
• Define them using the fully qualified attr function.

this may break applications that have been using earlier macros. While existing macros can be kept, it's better to clean up as the impact is minimal.

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 #1140 (a71f5e2) into main (3701a6e) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1140      +/-   ##
==========================================
- Coverage   93.39%   93.38%   -0.01%     
==========================================
  Files         165      165              
  Lines        6229     6230       +1     
==========================================
  Hits         5817     5817              
- Misses        412      413       +1     

Impacted Files	Coverage Δ
...y/sdk/resource/experimental_semantic_conventions.h	100.00% <ø> (ø)
sdk/src/resource/resource.cc	96.78% <100.00%> (+0.11%)	⬆️
sdk/test/resource/resource_test.cc	93.81% <100.00%> (ø)
...include/opentelemetry/sdk/common/circular_buffer.h	97.92% <0.00%> (-2.08%)	⬇️

[esigo]

LGTM