[sdk-metrics] XML doc tweaks for exemplar experimental APIs

[CodeBlanch]

Changes

• A little cleanup and improvement for the XML docs provided for the exemplar experimental APIs.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.18%. Comparing base (6250307) to head (313715c).
Report is 100 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5392      +/-   ##
==========================================
- Coverage   83.38%   83.18%   -0.20%     
==========================================
  Files         297      284      -13     
  Lines       12531    12049     -482     
==========================================
- Hits        10449    10023     -426     
+ Misses       2082     2026      -56     

Flag	Coverage Δ
unittests	?
unittests-Solution-Experimental	83.15% <ø> (?)
unittests-Solution-Stable	83.13% <ø> (?)

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

Files	Coverage Δ
.../Metrics/Builder/MeterProviderBuilderExtensions.cs	100.00% <ø> (ø)
...xemplar/AlignedHistogramBucketExemplarReservoir.cs	80.00% <ø> (-12.86%)	⬇️
...emetry/Metrics/Exemplar/AlwaysOffExemplarFilter.cs	0.00% <ø> (ø)
...lemetry/Metrics/Exemplar/AlwaysOnExemplarFilter.cs	100.00% <ø> (ø)
src/OpenTelemetry/Metrics/Exemplar/Exemplar.cs	91.11% <ø> (-8.89%)	⬇️
...nTelemetry/Metrics/Exemplar/ExemplarMeasurement.cs	100.00% <ø> (ø)
...penTelemetry/Metrics/Exemplar/ExemplarReservoir.cs	100.00% <ø> (ø)
...try/Metrics/Exemplar/ReadOnlyExemplarCollection.cs	78.26% <ø> (ø)
...trics/Exemplar/SimpleFixedSizeExemplarReservoir.cs	87.50% <ø> (ø)
...metry/Metrics/Exemplar/TraceBasedExemplarFilter.cs	0.00% <ø> (ø)
... and 1 more

... and 50 files with indirect coverage changes