VMR output and intermediate directory names need a rework

[mmitche]

Describe the Bug

When working on a cross-build for Linux, @directhex noted that the blob feed and artifacts directories still specify x64: #3671 (comment). We should rework these directory names.

Steps to Reproduce

See #3671 (comment) for info.

Other Information

My guess is that the target arch should be in the name of the directory, rather than the host. Furthermore, it may make sense to change 'blob-feed' to something meaningful (intermediate-assets?). 'blob-feed' refers to a bit of ancient technology we used to use for NuGet feeds in the 2.1 timeframe (Sleet).

T-Shirt size: XS

[mmitche]

T-Shirt size: Small, not critical

These changes should be relatively simple?

[ViktorHofer]

Note that TargetArchitecture is already encoded in the directory name. I think this issue comes from not using the GNU terms correctly in the various repositories and now also having a OverrideTargetOS setting. We should simplify those various models. I expect the folder structure to be automatically fixed when doing that.

Overall I agree that what this issue tracks is not critical and just a cosmetic change.

[ViktorHofer]

I think it would make sense to sit down with @directhex and some others to discuss all the OS and arch properties that we plan to pass in. @mmitche has a proposal for source build controls and while that's great for all the various source build specifics, I see value in having a separate discussion about the OS and arch combinations especially to support cross builds.

Here's what I implemented for the Windows PoC: https://github.com/dotnet/dotnet/blob/37cd6b020dda102b265ff62577a02f580230fa21/Directory.Build.props#L8-L54