[API] Parse baggage value as spec compliant

[ThomsonTan]

Fixes #3754

Changes

Please provide a brief description of the changes here.

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[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 89.94%. Comparing base (b568e71) to head (d4bf0e4). :warning: Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3758      +/-   ##
==========================================
+ Coverage   89.93%   89.94%   +0.01%     
==========================================
  Files         225      225              
  Lines        7158     7163       +5     
==========================================
+ Hits         6437     6442       +5     
  Misses        721      721              

Files with missing lines	Coverage Δ
api/include/opentelemetry/baggage/baggage.h	98.20% <100.00%> (+0.91%)	:arrow_up:

... and 4 files with indirect coverage changes

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