dotnet clean should be more resilient to TFM changes

[baronfel]

Is your feature request related to a problem? Please describe.

When users change their projects to add new TFMs, artifacts from prior TFMs can remain in the intermediate directories. This can result in various build processes mistakenly reading those artifacts. Users may then attempt a dotnet clean operation, which doesn't clean up artifacts from the previous TFMs due to the way that the list of items to clean is populated in the targets.

Describe the solution you'd like

We should provide an easy, comprehensive way to clean out the intermediate directories for project(s) or a solution that works independently of the TFM(s) provided to the command. It might be as simple as having an --all option added to dotnet clean, or as drastic as making the default behavior of dotnet clean this more broad removal. After the command is run, no artifacts from any TFM(s) should be present in the any of the IntermediateOutputPath(s) of the projects or solutions.

[danroth27]

Example quote from a customer hitting issues with this: "Yesterday I had to reinstall my VS installation for the intellisense to understand that project was an Blazor app. Then I had to research internet, then some smart one pointed out that I should remove /obj folder in solution folder. I did it and everything worked. 5 hours thrown away for nothing, I expected that 'Clean solution' would Clean up temp files, or I’m wrong?"