Add support for running with tfm=net9.0

[radical]

• ChannelMap: add entry for 9.0
• nuget.config: add dotnet9 source
• Add 9.0 versions for package references

[radical]

Don't merge yet.

[radical]

Related PR - dotnet/BenchmarkDotNet#2447 .

[radical]

@LoopedBard3 @cincuranet could we get the latest BDN package published to the nuget feed?

error NU1102: Unable to find package BenchmarkDotNet.Diagnostics.Windows with version (>= 0.13.10-nightly.20231019.90)
error NU1102:   - Found 49 version(s) in benchmark-dotnet-prerelease [ Nearest version: 0.13.9-nightly.20230908.70 ] 

[LoopedBard3]

@radical the 0.13.10-nightly.20231019.90 version should now be available.

[LoopedBard3]

LGTM

[radical]

Failure is relevant, investigating now.

[DrewScoggins]

Should we also go ahead and add all of the release/9.0* branches as well?

[radical]

The blazor_scenarios fails with:
[2023/10/19 18:04:43][INFO] /datadisks/disk1/work/BA02099F/p/artifacts/packages/microsoft.net.sdk.webassembly.pack/9.0.0-alpha.1.23470.17/build/Microsoft.NET.Sdk.WebAssembly.Browser.targets(157,38): error MSB4057: The target "WasmBuildApp" does not exist in the project. [/datadisks/disk1/work/BA02099F/w/AFEA0949/e/app/BlazingPizza.Client/BlazingPizza.Client.csproj::TargetFramework=net9.0]

.. which is because the latest sdk still has a much older WorkloadManifest (note 9.0.0-alpha.1.23470.17 in the path) which is missing bunch of changes needed to support building with net9.0, thus the webassembly.sdk is not imported and we get this error.
This will have to be ignored for now, as the the flow of runtime through to installer is stuck right now. But we can validate the changes with a run on dotnet-runtime-perf.

The sdk_scenarios failures are not related, IIUC.

[radical]

A new installer is available, so I triggered a rebuild.

[radical]

All the blazor_scenarios pass now with the new installer! Only unrelated failures are left.