[5.1] Add | Cache TokenCredential objects to take advantage of token caching (#2380)

[dauinsight]

Backports: #2380

[codecov]

Codecov Report

Attention: Patch coverage is 82.10526% with 17 lines in your changes missing coverage. Please review.

Project coverage is 71.95%. Comparing base (6fe8e21) to head (dc6e465).
Report is 1 commits behind head on release/5.1.

Files	Patch %	Lines
...SqlClient/ActiveDirectoryAuthenticationProvider.cs	82.10%	17 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           release/5.1    #2776      +/-   ##
===============================================
+ Coverage        71.88%   71.95%   +0.07%     
===============================================
  Files              293      293              
  Lines            61574    61643      +69     
===============================================
+ Hits             44261    44355      +94     
+ Misses           17313    17288      -25     

Flag	Coverage Δ
addons	92.38% <ø> (ø)
netcore	76.00% <82.10%> (+<0.01%)	⬆️
netfx	69.65% <82.10%> (+0.10%)	⬆️

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