vscode: add launch.json to test extension

Summary:
This provides a way to launch a vscode instance that has the extension
and with a debugger.

Reviewed By: evangrayk

Differential Revision: D53958066

fbshipit-source-id: df023bae9eedc5fe41f1fd630096211fed558330

addons/vscode/.vscode/launch.json

@@ -0,0 +1,14 @@
+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "Run Extension",
+            "type": "extensionHost",
+            "request": "launch",
+            "runtimeExecutable": "${execPath}",
+            "args": [
+                "--extensionDevelopmentPath=${workspaceFolder}"
+            ],
+        }
+    ]
+}