`dotnet workload clean --all` should remove all workload artifacts to help recover from bad states

[nagilson]

Summary

dotnet workload clean --all should be enhanced to remove all workload-related artifacts on disk, including workload sets json files and manifests, to help users fully recover from corrupted or bad workload states.

Background

While working on #52434 (fixing workload repair to handle missing manifests), I observed that it's very difficult for users to recover from certain bad workload states.

For example, say a package manager deletes a manfiest file. Then, if a user deletes the sdk-manifests folder manually to try to fix this, this isn't sufficient to reset workloads to a clean state—somewhere on disk, the SDK still thinks workloads are installed. Users currently have no reliable way to get back to a "blank slate" for workloads.

Problem

dotnet workload clean --all does not remove all workload-related components:

• Workload sets may remain on disk
• Other artifacts that track installed workload state persist
• Users can get stuck in states where workloads appear installed but are broken

Proposed Solution

Enhance dotnet workload clean --all to:

1. Remove workload sets
2. Remove all manifest-related files
3. Clear any other persisted state that tracks installed workloads
4. Effectively restore the SDK to a state as if no workloads were ever installed

This would give users a reliable escape hatch when workloads get into a bad state, rather than requiring manual hunting for files across the disk.

Additional Context

• Related PR: workload repair can recover from corrupt workload sets #52434 (workload repair for missing manifests)
• The --all flag already implies a more aggressive cleanup, so this enhancement aligns with user expectations