[release/9.0] Add System.Security.Cryptography.Xml 8.0.4

[wtgodbe]

Adds the source-built reference package for System.Security.Cryptography.Xml 8.0.4.

• Uses the existing source-built System.Security.Cryptography.Pkcs 8.0.1 dependency; no additional System.Security.Cryptography packages are required.
• Carries forward the IndexerName metadata fix from [release/9.0] Add patched 8.0 system.security.cryptography packages #1676.
• Registers the package as a DependencyPackageProject.

Validation:

• Targeted source-build completed successfully and produced System.Security.Cryptography.Xml.8.0.4.nupkg for net6.0, net7.0, net8.0, and netstandard2.0.
• The full inner source-build completed successfully. The final prebuilt-baseline check on macOS reports the host-specific runtime.osx-arm64 ILAsm/ILDAsm packages; product source-build is supported on Linux.