Change locks to System.Threading.Lock

[JeremyKuhne]

Change internal lock objects to System.Threading.Lock

Fixes #11672

Microsoft Reviewers: Open in CodeFlow

[lonitra]

LGTM Minor comment, but can be addressed in the next.

[codecov]

Codecov Report

Attention: Patch coverage is 83.63636% with 9 lines in your changes missing coverage. Please review.

Project coverage is 75.00413%. Comparing base (7aeab49) to head (baad52b).
Report is 44 commits behind head on feature/10.0.

Additional details and impacted files

@@                  Coverage Diff                   @@
##           feature/10.0      #11841         +/-   ##
======================================================
- Coverage      75.30464%   75.00413%   -0.30052%     
======================================================
  Files              3039        3035          -4     
  Lines            645429      630232      -15197     
  Branches          50777       46683       -4094     
======================================================
- Hits             486038      472700      -13338     
+ Misses           155909      154187       -1722     
+ Partials           3482        3345        -137     

Flag	Coverage Δ
Debug	75.00413% <83.63636%> (-0.30052%)	⬇️
integration	17.95314% <62.26415%> (-1.50399%)	⬇️
production	48.11162% <84.90566%> (-1.38449%)	⬇️
test	97.01069% <50.00000%> (-0.04806%)	⬇️
unit	45.13556% <81.13208%> (-1.36739%)	⬇️

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