Merged PoolWaitHandles, DbConnectionPoolIdentity, removed DbBuffer

[edwardneal]

Contributes to #1261.

This is a little more involved than the previous merges. PoolWaitHandles and DbConnectionPoolIdentity in .NET Framework currently use direct PInvoke to wait on named objects and get the Windows identity details. I've merged these with their .NET Core counterparts, which behave the same way.

Doing so also removes the last reference to DbBuffer, which was only present in the .NET Framework project. With those references gone, I've removed this too. This contributes to three quarters of the deletions - the PR's a fair bit smaller than it looks!

[codecov]

Codecov Report

Attention: Patch coverage is 93.93939% with 2 lines in your changes missing coverage. Please review.

Project coverage is 72.04%. Comparing base (619fa74) to head (b645fea).
Report is 5 commits behind head on main.

Files	Patch %	Lines
...rc/Microsoft/Data/ProviderBase/DbConnectionPool.cs	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2390      +/-   ##
==========================================
+ Coverage   71.66%   72.04%   +0.38%     
==========================================
  Files         308      305       -3     
  Lines       62297    61804     -493     
==========================================
- Hits        44646    44529     -117     
+ Misses      17651    17275     -376     

Flag	Coverage Δ
addons	92.90% <ø> (ø)
netcore	75.91% <86.66%> (-0.01%)	⬇️
netfx	70.22% <76.00%> (+0.56%)	⬆️

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[DavoudEshtehari]

@edwardneal Can you address the conflicts, please?

[edwardneal]

Thanks @DavoudEshtehari. I've handled the merge conflicts, and the test failure seems to be unrelated to me.

[DavoudEshtehari]

Given these changes, I believe the DbConnectionPool.NetCoreApp.cs file can be merged with the other files to make it simpler to follow. It's not a critical change request, but it would be nice to have.

[edwardneal]

I agree. I've moved the method into DbConnectionPool.cs and guarded it behind #if NET6_0_OR_GREATER to make the later merge simpler.