proxy_agent: Use proxy-from-env for robustness

Now we support pretty much every variable under the sun along with
$NO_PROXY all correctly and with minimal code on our end.

lib/vscode/package.json

@@ -65,6 +65,7 @@
     "native-watchdog": "1.3.0",
     "node-pty": "0.10.0-beta17",
     "proxy-agent": "^4.0.0",
+    "proxy-from-env": "^1.1.0",
     "rimraf": "^2.2.8",
     "spdlog": "^0.11.1",
     "sudo-prompt": "9.1.1",
@@ -95,6 +96,7 @@
     "@types/minimist": "^1.2.0",
     "@types/mocha": "2.2.39",
     "@types/node": "^12.11.7",
+    "@types/proxy-from-env": "^1.0.1",
     "@types/sinon": "^1.16.36",
     "@types/trusted-types": "^1.0.6",
     "@types/vscode-windows-registry": "^1.0.0",