debug: make auto attach apply state transition in new workspaces

Previous there was a case:

1. Auto attach was enabled in user settings and workspace A was open
2. Switch to workspace B, and then turn auto attach off in user settings
3. Switching back to workspace A, environment variables were not cleared

Now, the last state is stored in the workspace settings so that
we can tear down the previous state if necessary.

extensions/debug-auto-launch/.vscode/launch.json

@@ -0,0 +1,20 @@
+{
+  // Use IntelliSense to learn about possible attributes.
+  // Hover to view descriptions of existing attributes.
+  // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "name": "Extension",
+      "type": "extensionHost",
+      "request": "launch",
+      "skipFiles": ["<node_internals>/**"],
+      "args": [
+        "--extensionDevelopmentPath=${workspaceFolder}",
+      ],
+      "outFiles": [
+        "${workspaceFolder}/out/**/*.js",
+      ],
+    }
+  ]
+}