VS Code: add a debug configuration to debug the tests

This is _very_ convenient: just select the "Debug" panel on the left
side of the VS Code window, select the `Debug Tests` in the drop-down
box at the top of said panel, set breakpoints at your heart's extent and
start debugging interactively, with the ability to inspect local
variables and single-stepping.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.vscode/launch.json

@@ -1,6 +1,17 @@
 {
   "version": "0.2.0",
   "configurations": [
+    {
+      "type": "node",
+      "request": "launch",
+      "name": "Debug Tests",
+      "program": "${workspaceRoot}/node_modules/.bin/jest",
+      "cwd": "${workspaceRoot}",
+      "args": ["--runInBand", "--config", "jest.config.js"],
+      "windows": {
+        "program": "${workspaceFolder}/node_modules/jest/bin/jest"
+      }
+    },
     {
       "name": "Attach to Node Functions",
       "type": "node",
@@ -9,4 +20,4 @@
       "preLaunchTask": "func: host start"
     }
   ]
-}
+}