Refactor Metrics code for Exemplars

[utpilla]

Changes

• Remove unnecessary isSampled parameter for Exemplars

Hide whitespaces from the diff for easier review of the code:

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.66%. Comparing base (6250307) to head (33e5e00).
Report is 105 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5401      +/-   ##
==========================================
+ Coverage   83.38%   84.66%   +1.27%     
==========================================
  Files         297      281      -16     
  Lines       12531    11457    -1074     
==========================================
- Hits        10449     9700     -749     
+ Misses       2082     1757     -325     

Flag	Coverage Δ
unittests	?
unittests-Solution-Experimental	84.59% <100.00%> (?)
unittests-Solution-Stable	84.64% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/OpenTelemetry/Metrics/AggregatorStore.cs	82.48% <100.00%> (+2.09%)	⬆️
src/OpenTelemetry/Metrics/MetricPoint.cs	92.73% <100.00%> (+24.25%)	⬆️

... and 75 files with indirect coverage changes

[utpilla]

Check this comment: #5399 (comment)