Preserve distributed transactions on pooled connection reset

[mdaigle]

The current behavior only preserves transaction state for the root transaction. Enlisted connections that are reset will be placed in the transacted connection pool, but in some situations, will no longer participate in the transaction. The next connection to request the connection will expect it to be participating in the transaction, but actions on the connection will auto-commit.

This changes the reset logic to preserve transaction state for enlisted connections (part of a distributed transaction, but not root).

[mdaigle]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.69%. Comparing base (b1f7eaf) to head (6db966b).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3019   +/-   ##
=======================================
  Coverage   72.68%   72.69%           
=======================================
  Files         285      285           
  Lines       59155    59161    +6     
=======================================
+ Hits        42998    43005    +7     
+ Misses      16157    16156    -1     

Flag	Coverage Δ
addons	92.58% <ø> (ø)
netcore	75.40% <100.00%> (+0.01%)	⬆️
netfx	71.13% <100.00%> (+<0.01%)	⬆️

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