[WIP] Refactoring trace state

[nikhil1511]

Fixes #79

• Refactoring trace state code to reuse functionality in baggage implementation
• Extracted common parsing logic of headers from trace_state into kv_properties

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

[linux-foundation-easycla]

• ✅ nikhil1511 (e5d39c0)

• ❌ The commit (432a8c8 ,a452a20babcc30050d30eefa95d5e7d27dc22e98 ,d01a4e38632f4862d608ec5e30af830386e3c70e) is missing the User's ID, preventing the EasyCLA check. Consult GitHub Help to resolve.For further assistance with EasyCLA, please submit a support request ticket.

[codecov]

Codecov Report

Merging #637 (d01a4e3) into main (9fa6bd5) will increase coverage by 0.03%.
The diff coverage is 97.20%.

❗ Current head d01a4e3 differs from pull request most recent head e5d39c0. Consider uploading reports for the commit e5d39c0 to get more accurate results

@@            Coverage Diff             @@
##             main     #637      +/-   ##
==========================================
+ Coverage   94.49%   94.52%   +0.03%     
==========================================
  Files         197      199       +2     
  Lines        9130     9135       +5     
==========================================
+ Hits         8627     8635       +8     
+ Misses        503      500       -3     

Impacted Files	Coverage Δ
api/include/opentelemetry/common/string_util.h	66.66% <66.66%> (ø)
api/include/opentelemetry/trace/trace_state.h	98.80% <98.14%> (+1.26%)	⬆️
api/include/opentelemetry/common/kv_properties.h	98.27% <98.27%> (ø)
api/test/trace/trace_state_test.cc	100.00% <100.00%> (+2.22%)	⬆️
sdk/src/logs/batch_log_processor.cc	95.00% <0.00%> (+1.25%)	⬆️