add System.Diagnostics.DiagnosticSource 9.0.0

[JanProvaznik]

Needed for MSBuild telemetry investments. dotnet/msbuild#11169

1. ./generate.sh --package System.Diagnostics.DiagnosticSource,9.0.0
2. add DependencyPackageProjects to eng/Build.props

[MichaelSimons]

This can't be added. I think I know how to fix this and will push a fix.

[JanProvaznik]

@dotnet/source-build I did quite weird stuff to get this PR green, please review how it should be done correctly.

1. it failed upon seeing the scoped keywords in the generated files https://github.com/dotnet/source-build-reference-packages/pull/1101/checks?check_run_id=34712767234 fixed by: c48afa6 (#1101) c162c9b (#1101)
2. It failed with error CS0518: Predefined type 'System.Runtime.CompilerServices.IsExternalInit' is not defined or imported https://github.com/dotnet/source-build-reference-packages/pull/1101/checks?check_run_id=34714580836 resolved by c162c9b (#1101)
3. a prebuilt was reported for microsoft.netcore.app.ref which in fact exists in the repo https://github.com/dotnet/source-build-reference-packages/tree/main/src/targetPacks/ILsrc/microsoft.netcore.app.ref , resolved by 40967d8 (#1101)

[MichaelSimons]

3. a prebuilt was reported for microsoft.netcore.app.ref which in fact exists in the repo https://github.com/dotnet/source-build-reference-packages/tree/main/src/targetPacks/ILsrc/microsoft.netcore.app.ref , resolved by 40967d8 (#1101)

I think I took care of this in 1de36a7

[MichaelSimons]

It failed with error CS0518: Predefined type 'System.Runtime.CompilerServices.IsExternalInit' is not defined or imported https://github.com/dotnet/source-build-reference-packages/pull/1101/checks?check_run_id=34714580836 resolved by c162c9b (#1101)

This is a known problem tracked with dotnet/source-build#4159. We have a common shared file with the type in it. I update the project to reference it.