Describe the solution you'd like

In .NET 6 we added support for implied/partial RIDs, as well as flags for specifying the OS portions of a RID. If this flag are specified, any missing RID portions are inferred from the current SDK execution context. For example, dotnet publish --os linux run on an x64 Windows system results in a final RID of linux-x64.

This support exists already in the dotnet build command. We should also support this flags on the restore command, since it already allows for RID-specific restores via the -r/--runtime flag. This should be done similar to the existing dotnet restore --arch flag.