[sdk-metrics] Refactor duplicated update completion code into a helper in MetricPoint

[CodeBlanch]

Changes

• Fix a few violations of DRY by introducing a helper method for update completion code 😄

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.54%. Comparing base (6250307) to head (1277a09).
Report is 104 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5398      +/-   ##
==========================================
+ Coverage   83.38%   84.54%   +1.16%     
==========================================
  Files         297      284      -13     
  Lines       12531    12096     -435     
==========================================
- Hits        10449    10227     -222     
+ Misses       2082     1869     -213     

Flag	Coverage Δ
unittests	?
unittests-Solution-Experimental	84.52% <100.00%> (?)
unittests-Solution-Stable	84.29% <100.00%> (?)

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

Files	Coverage Δ
src/OpenTelemetry/Metrics/MetricPoint.cs	92.81% <100.00%> (+24.34%)	⬆️

... and 54 files with indirect coverage changes