Bug: fix naming, order and formatting for diagnostics

[Wraith2]

Fixes #1634

We were not being consistent about calling diagnostic message output functions before we set the result/exception/cancel methods on the TaskCompletionSource that the users is waiting on. This allowed a rare race condition to occur in libraries consuming diagnostic events and attempting to correlate it to their own current context.

This PR does 3 things:

1. ensures that all disgnostic message methods in async methods are called before tcs methods.
2. changes the name of the diagnostic source to be consistent with the other uses in the library and the applivable naming rules, it should be s_diagnosticListener not _diagnosticListener
3. reformats the task continuation lambdas so it's clearer to understand the scope.

N.B. netfx does not use diagnostics so no changes are required for that part of the project.

/cc @okolvik-avento if possible you could try the output artifacts nuget package once the CI run has completed?

[codecov]

Codecov Report

Merging #1637 (530de53) into main (9b1996a) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1637      +/-   ##
==========================================
+ Coverage   71.30%   71.32%   +0.02%     
==========================================
  Files         295      295              
  Lines       61195    61205      +10     
==========================================
+ Hits        43637    43657      +20     
+ Misses      17558    17548      -10     

Flag	Coverage Δ
addons	92.38% <ø> (ø)
netcore	74.84% <100.00%> (-0.06%)	⬇️
netfx	69.24% <ø> (+0.09%)	⬆️

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

Impacted Files	Coverage Δ
...netcore/src/Microsoft/Data/SqlClient/SqlCommand.cs	83.64% <100.00%> (+0.05%)	⬆️
...ActiveDirectoryAuthenticationTimeoutRetryHelper.cs	56.81% <0.00%> (-6.82%)	⬇️
...rc/Microsoft/Data/SqlClient/SQLFallbackDNSCache.cs	90.62% <0.00%> (-6.25%)	⬇️
...re/src/Microsoft/Data/SqlClient/SNI/SNINpHandle.cs	73.29% <0.00%> (-5.12%)	⬇️
...osoft/Data/SqlClient/SqlConnectionStringBuilder.cs	87.94% <0.00%> (-0.41%)	⬇️
...crosoft/Data/SqlClient/SqlInternalConnectionTds.cs	73.12% <0.00%> (-0.30%)	⬇️
.../netcore/src/Microsoft/Data/SqlClient/TdsParser.cs	73.70% <0.00%> (-0.05%)	⬇️
...nt/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs	70.98% <0.00%> (-0.02%)	⬇️
...crosoft/Data/SqlClient/SqlInternalConnectionTds.cs	68.05% <0.00%> (+0.08%)	⬆️
...ient/netfx/src/Microsoft/Data/SqlClient/SqlUtil.cs	58.36% <0.00%> (+0.24%)	⬆️
... and 3 more

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[okolvik-avento]

@Wraith2 Running tests now

[okolvik-avento]

@Wraith2 Works great! No exceptions after over 500k requests.

[okolvik-avento]

Over 5 million requests now without exceptions

[David-Engel]

LGTM