Feature request: in-place, upgradeable installers

[natemcmaster]

Is your feature request related to a problem? Please describe.
Old versions of .NET Core are taking a lot of disk space on my dev machine. This is in part because Visual Studio so rapidly updates and automatically brings in new .NET Core versions.

Runtime: I don't need most of them because the runtime will auto-rollforward to latest patched versions.
SDK: because the SDK is highly backwards compatible, I generally don't use global.json because the latest stable SDK works well for most projects.

Describe the solution you'd like
I'd like a way to have the Windows installers upgrade in place and trim unused older runtimes and SDKs. I'd also like a way to cleanup unsued packages from C:\Program Files\dotnet\sdk\NuGetFallbackFolder.

Describe alternatives you've considered

• The runtime and SDK installers could use MSI to do the in-place upgrade
• Provide a tool such as dotnet-uninstaller which can trim unused versions of the runtime/SDK.
• Provide a tool to cleanup C:\Program Files\dotnet\sdk\NuGetFallbackFolder to remove packages matching unused, old runtimes

Additional context

[leecow]

moving to core-setup

[leecow]

Issue moved to dotnet/core-setup #4188 via ZenHub

[natemcmaster]

While it certainly applies to core-setup, I think this applies more broadly. If we do this, it applies to dotnet/cli and aspnet as well.