[Signing] Sign newly bundled mlaunch assemblies (#26751)

The Sign Archives job in Azure DevOps build 15470839 fails when signing
package contents. Both the iOS and tvOS mlaunch.app MonoBundle now
contain System.Drawing.dll, System.Drawing.Primitives.dll, and
System.IO.Pipelines.dll, but the signing list does not classify them.
The signing task therefore rejects all six copies as unknown files.

Classify these .NET assemblies as FirstParty alongside the other mlaunch
framework assemblies so the packages can be signed.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 5965bad4-5f96-4bf5-8b2d-a55ecd3d2ea9

Author: dalexsoto

dotnet/Workloads/SignList.xml

@@ -101,11 +101,14 @@
     <FirstParty Include="System.Diagnostics.DiagnosticSource.dll" />
     <FirstParty Include="System.Diagnostics.Process.dll" />
     <FirstParty Include="System.Diagnostics.StackTrace.dll" />
+    <FirstParty Include="System.Drawing.Primitives.dll" />
+    <FirstParty Include="System.Drawing.dll" />
     <FirstParty Include="System.dll" />
     <FirstParty Include="System.Formats.Asn1.dll" />
     <FirstParty Include="System.IO.Compression.Brotli.dll" />
     <FirstParty Include="System.IO.Compression.dll" />
     <FirstParty Include="System.IO.MemoryMappedFiles.dll" />
+    <FirstParty Include="System.IO.Pipelines.dll" />
     <FirstParty Include="System.IO.Pipes.dll" />
     <FirstParty Include="System.Linq.dll" />
     <FirstParty Include="System.Memory.dll" />