Accelerate local builds in Visual Studio

[christophwille]

https://github.com/dotnet/project-system/blob/main/docs/build-acceleration.md

<ProduceReferenceAssembly>true<ProduceReferenceAssembly> is necessary in our case because of ics.d being netstandard2.0, otherwise this error shows up for FUTD:

4>FastUpToDate: Comparing timestamps of inputs and outputs: (ICSharpCode.ILSpyX)
4>FastUpToDate:     Adding UpToDateCheckBuilt outputs: (ICSharpCode.ILSpyX)
4>FastUpToDate:         D:\GitWorkspace\ILSpy\ICSharpCode.ILSpyX\bin\Debug\net6.0\ICSharpCode.ILSpyX.dll (ICSharpCode.ILSpyX)
4>FastUpToDate: Output 'D:\GitWorkspace\ILSpy\ICSharpCode.ILSpyX\bin\Debug\net6.0\ICSharpCode.ILSpyX.dll' does not exist, not up-to-date. (ICSharpCode.ILSpyX)
4>FastUpToDate: This project has enabled build acceleration, but not all referenced projects produce a reference assembly. Ensure projects producing the following outputs have the 'ProduceReferenceAssembly' MSBuild property set to 'true': 'D:\GitWorkspace\ILSpy\ICSharpCode.Decompiler\bin\Debug\netstandard2.0\ICSharpCode.Decompiler.dll'. See https://aka.ms/vs-build-acceleration for more information. (ICSharpCode.ILSpyX)
4>FastUpToDate: Up-to-date check completed in 0.3 ms (ICSharpCode.ILSpyX)