Replace internal BouncyCastle with NuGet package (#1370)

* Replace internal BouncyCastle with NuGet package

* fix NullReference in KeyExchangeECDH

for some reason d24fe20 introduced
its own names here which (as far as I can see) were never part
of the original BouncyCastle.

Switched to the correct names.

* Update to BouncyCastle 2.3.1

* Update to BouncyCastle 2.4.0

* fix Conflict between Zlib class and BouncyCastle namespace

CA1724: The type name Zlib conflicts in whole or in part with the namespace name 'Org.BouncyCastle.Utilities.Zlib'. Change either name to eliminate the conflict.

We can't change either, so suppress the warning.

---------

Co-authored-by: Rob Hague <rob.hague00@gmail.com>

Author: mus65

src/Renci.SshNet/Compression/Zlib.cs

@@ -7,7 +7,9 @@ namespace Renci.SshNet.Compression
     /// <summary>
     /// Represents the "zlib" compression algorithm.
     /// </summary>
+#pragma warning disable CA1724 // Type names should not match namespaces
     public class Zlib : Compressor
+#pragma warning restore CA1724 // Type names should not match namespaces
     {
         private readonly ZLibStream _compressor;
         private readonly ZLibStream _decompressor;

src/Renci.SshNet/Renci.SshNet.csproj

@@ -40,6 +40,10 @@
     <PackageReference Include="System.Memory" Version="4.5.5" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="BouncyCastle.Cryptography" Version="[2.4.0,)" />
+  </ItemGroup>
+
   <ItemGroup>
     <None Include="..\..\images\logo\png\SS-NET-icon-h500.png">
       <Pack>True</Pack>