Merge common code bases for TdsParserStateObject.cs (5)

[panoskj]

This is a draft PR as I intend to add a few more commits. But let me know if you think this should be merged by itself.

So, in this comment, I asked about ValidateSNIConnection (3rd question, 4 possible solutions are suggested). @David-Engel responded and it looks like we both agree on the implementation of this PR.

To sum up, this PR effectively changes the implementation of IsConnectionAlive in netfx to check if the handle is null before passing it to SNICheckConnection. If it is null, the connection will be considered alive. This behavior is in line with netcore implementation for native.

Moreover, it appears that:

1. Native SNICheckConnection doesn't expect null values.
2. The handle in question will only be null if the TdsParserStateObject has been disposed.
3. We assume IsConnectionAlive is not called if TdsParserStateObject has been disposed (otherwise you would have noticed the bug already).

Therefore, an even better implementation would be to throw an exception (or at least use a debug assertion) to make sure the handle is never null when CheckConnection is called. Note that netcore already does this for the managed implementation (which reinforces the assumption (3)). The null check below the linked line is redundant by the way (I guess the null check predated throwing the exception).

Let me know what you think @Wraith2 @DavoudEshtehari @JRahnama @David-Engel

[codecov]

Codecov Report

Attention: 35 lines in your changes are missing coverage. Please review.

Comparison is base (b12b15d) 72.57% compared to head (3354c9c) 66.67%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
...c/Microsoft/Data/SqlClient/TdsParserStateObject.cs	86.28%	31 Missing ⚠️
...osoft/Data/SqlClient/TdsParserStateObject.netfx.cs	89.28%	3 Missing ⚠️
...oft/Data/SqlClient/TdsParserStateObject.netcore.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2302      +/-   ##
==========================================
- Coverage   72.57%   66.67%   -5.90%     
==========================================
  Files         310      304       -6     
  Lines       62065    61544     -521     
==========================================
- Hits        45041    41036    -4005     
- Misses      17024    20508    +3484     

Flag	Coverage Δ
addons	∅ <ø> (∅)
netcore	70.84% <86.26%> (-5.89%)	⬇️
netfx	64.36% <86.97%> (-5.60%)	⬇️

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