Align ADP.IsEmpty -> string.IsNullOrEmpty

[MichelZ]

This PR simply changes ADP.IsEmpty to string.IsNullOrEmpty to align netfx with netcore

Part of #2953

[benrr101]

Why this method exists, I have no idea. I will look forward to removing it soon enough.

[MichelZ]

@cheenamalhotra Could you also run this pipeline? Thx :)

[cheenamalhotra]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[ErikEJ]

@benrr101 IsNullOrEmpty did not exist in .NET Framework 1 😅

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 72.34%. Comparing base (9d5ca32) to head (b20df43).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
...nt/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2961      +/-   ##
==========================================
+ Coverage   72.31%   72.34%   +0.02%     
==========================================
  Files         288      288              
  Lines       59660    59660              
==========================================
+ Hits        43145    43162      +17     
+ Misses      16515    16498      -17     

Flag	Coverage Δ
addons	92.58% <ø> (ø)
netcore	75.39% <ø> (-0.04%)	⬇️
netfx	70.76% <71.42%> (+0.08%)	⬆️

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