Describe the bug

When opening the test explorer in a mult-root workspace, each root contains a copy of all tests available in the workspace.

To Reproduce

1. Open vscode starter workspace
2. Open test explorer view
3. Refresh
4. Expand any two root folders

Notice that the two roots have duplicated sub-folders.

Expected behavior

Sub-folders should not be duplicated across workspace roots.

Additional context

There might be a way to think of this as a feature, not a bug. It might be the case that tests run in the context of different workspace roots will behave differently, so maybe we want to allow this duplication.