Fix DAC connections to localhost in managed SNI

[David-Engel]

Fixes #1772. When connecting to the DAC port, the previous code was converting localhost to Environment.MachineName. Native SNI does it the other way around. It converts Environment.MachineName to localhost.

[codecov]

Codecov Report

Base: 70.68% // Head: 70.21% // Decreases project coverage by -0.46% ⚠️

Coverage data is based on head (a1651a5) compared to base (22eb6c7).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1865      +/-   ##
==========================================
- Coverage   70.68%   70.21%   -0.47%     
==========================================
  Files         292      292              
  Lines       61727    61728       +1     
==========================================
- Hits        43629    43341     -288     
- Misses      18098    18387     +289     

Flag	Coverage Δ
addons	92.38% <ø> (ø)
netcore	73.41% <100.00%> (-0.71%)	⬇️
netfx	69.07% <ø> (-0.09%)	⬇️

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

Impacted Files	Coverage Δ
...tcore/src/Microsoft/Data/SqlClient/SNI/SNIProxy.cs	77.06% <100.00%> (+0.80%)	⬆️
...c/Microsoft/Data/SqlClient/TdsParserStateObject.cs	23.30% <0.00%> (-21.08%)	⬇️
...ata/SqlClient/SqlConnectionTimeoutErrorInternal.cs	41.96% <0.00%> (-18.75%)	⬇️
...c/Microsoft/Data/Interop/SNINativeMethodWrapper.cs	75.43% <0.00%> (-1.01%)	⬇️
...c/Microsoft/Data/SqlClient/SqlConnectionFactory.cs	68.85% <0.00%> (-0.82%)	⬇️
...c/Microsoft/Data/SqlClient/TdsParserStateObject.cs	66.29% <0.00%> (-0.70%)	⬇️
...rc/Microsoft/Data/ProviderBase/DbConnectionPool.cs	85.19% <0.00%> (-0.67%)	⬇️
...nt/netcore/src/Microsoft/Data/SqlClient/SqlUtil.cs	48.90% <0.00%> (-0.48%)	⬇️
...icrosoft/Data/ProviderBase/DbConnectionInternal.cs	78.22% <0.00%> (-0.41%)	⬇️
...crosoft/Data/SqlClient/SqlInternalConnectionTds.cs	67.71% <0.00%> (-0.35%)	⬇️
... and 6 more

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