Two source-build prebuilts

[NikolaMilosavljevic]

This PR introduced 2 new prebuilts: #67333

    <Usage Id="Microsoft.AspNetCore.App.Ref" Version="8.0.0-preview.3.23164.14" />
    <Usage Id="Microsoft.NETCore.App.Ref" Version="8.0.0-preview.3.23165.3" />

Ref-pack versions are specified statically, in https://github.com/dotnet/roslyn/blob/main/eng/targets/Imports.BeforeArcade.targets

Package version properties should be used, instead:

MicrosoftAspNetCoreAppRefPackageVersion
MicrosoftNETCoreAppRefPackageVersion