Generated XCTest cases from build tool plugins are skipped or not discovered

## Summary Build-tool-plugin-generated XCTest methods are not handled consistently by the VS Code Swift extension. Using the attached reproduction package structure, generated tests may either: - be discovered but shown as **Skipped** - or not be discovered at all ## Reproduction Repository: https://github.com/tothambrus11/swift-vscode-test-discovery-problem-reproduction This mirrors `hylo-new` closely: - `CompilerTests` is an `XCTestCase` driver class - fixture directories under `Tests/CompilerTests/negative` and `Tests/CompilerTests/positive` are excluded from the test target - a `.buildTool` plugin generates `CompilerTests+GeneratedTests.swift` into the plugin work directory - the generated file adds `test_negative_*` / `test_positive_*` methods in an extension of `CompilerTests` ## Steps 1. Open the reproduction folder as the VS Code workspace root. 2. Enable the Swift extension. 3. Wait for package/test discovery. 4. Inspect the Testing sidebar. ## Actual behavior - Sometimes the generated tests are discovered but marked **Skipped**. - Sometimes the generated tests are not discovered. <img width="361" height="226" alt="Image" src="https://github.com/user-attachments/assets/03a35787-a5c2-4cb2-a409-6f55fb68fbc2" /> <img width="364" height="291" alt="Image" src="https://github.com/user-attachments/assets/8a02de8f-b04f-443b-b6ab-f18920fbf2b7" /> ## Expected behavior - The generated `test_negative_*` / `test_positive_*` XCTest methods should be discovered normally and should be runnable like regular XCTest methods. ## Notes - `swift test` on the CLI discovers and runs the generated tests successfully. - Reloading the VS Code window or cleaning the build folder may be needed to observe the change.