faster launch times for extension debugging (#1555)

* add a way to speed up subsequent launches of the extension.

* A cleaner way to exit

* update package.json

* read the environment variable to short-circuit the node_modules check.

Author: bobbrow

Extension/package.json

@@ -1047,7 +1047,7 @@
     "test": "gulp allTests",
     "tslint": "gulp tslint",
     "unitTests": "gulp unitTests",
-    "vscode:prepublish": "npm install && tsc -p ./ && node ./out/src/Debugger/copyScript.js",
+    "vscode:prepublish": "node ./src/Support/update.js && npm install && tsc -p ./ && node ./out/src/Support/copyDebuggerDependencies.js",
     "watch": "tsc -watch -p ./"
   },
   "devDependencies": {

Extension/src/Debugger/copyScript.ts renamed to Extension/src/Support/copyDebuggerDependencies.ts

@@ -0,0 +1,16 @@
+/* --------------------------------------------------------------------------------------------
+ * Copyright (c) Microsoft Corporation. All Rights Reserved.
+ * See 'LICENSE' in the project root for license information.
+ * ------------------------------------------------------------------------------------------ */
+'use strict';
+
+/**
+ * This file is used during local debugging of the extension and should not be referenced by any
+ * other source files.
+ */
+
+const fs = require("fs");
+if (!process.env.CPPTOOLS_DEV && fs.existsSync('./node_modules')) {
+    console.log("Skipping prepublish steps since they appear to have been executed already.");
+    process.exit(1);
+}