Make dotnet workload clean --all remove workload sets and manifests

[Copilot]

dotnet workload clean --all left workload sets and manifests on disk, preventing users from recovering from corrupted workload states.

Changes

• FileBasedInstaller: Added DeleteAllWorkloadSetsAndManifests() called when cleanAllPacks=true

  • Removes all workload sets from sdk-manifests/{featureBand}/workloadsets/
  • Removes all manifests from sdk-manifests/{featureBand}/{manifestId}/
  • Removes install state files (default.json)
  • Removes workload set and manifest installation records

• Test: Added GivenWorkloadCleanAllFileBasedItRemovesWorkloadSetsAndManifests covering both user-local and system-wide scenarios

• Localization: Added WorkloadCleanAllComplete resource string with xlf updates

• Unrelated fix: Corrected _testAssetsManager → TestAssetsManager in GivenDotnetSlnList (pre-existing bug blocking build)

Behavior

Before:

$ dotnet workload clean --all
# Removes packs only; workload sets and manifests remain

After:

$ dotnet workload clean --all
# Removes ALL workload artifacts across all feature bands
# SDK returns to state as if no workloads were installed

Original prompt

---

This section details on the original issue you should resolve

<issue_title>dotnet workload clean --all should remove all workload artifacts to help recover from bad states</issue_title>
<issue_description>## 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
  </issue_description>

<agent_instructions>dotnet workload clean was created before workload sets. Let's have the --all flag also remove all workload set information and see if that can help reset into the original state.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes dotnet workload clean --all should remove all workload artifacts to help recover from bad states #52701

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