Use the same Node version as VSCode

As recommended here #1369 (comment), we want to stay in sync with the current node version shipped with
VSCode (v16.13.0):

https://github.com/microsoft/vscode/blob/32d40cf44e893e87ac33ac4f08de1e5f7fe077fc/remote/.yarnrc#L2

For this we can add a `.nvmrc` file to alert nvm to switch to the preferred version automatically.

It will also help prevent builds from failing when setting up the project for the first time, as building the extension currently fails in Node v18: #1373

We're also updating the docs to mention using `nvm` to manage node versions and point to the right place to check for current supported versions.

Author: elenatanasoiu

CONTRIBUTING.md

@@ -29,7 +29,9 @@ Here are a few things you can do that will increase the likelihood of your pull
 
 ## Setting up a local build
 
-Make sure you have installed recent versions of vscode (>= v1.52), node (>=12.16), and npm (>= 7.5.2). Earlier versions will probably work, but we no longer test against them.
+Make sure you have installed recent versions of vscode, node, and npm. Check the `engines` block in [`package.json`](https://github.com/github/vscode-codeql/blob/main/extensions/ql-vscode/package.json) file for compatible versions. Earlier versions may work, but we no longer test against them.
+
+To automatically switch to the correct version of node, we recommend using [nvm](https://github.com/nvm-sh/nvm), which will pick-up the node version from `.nvmrc`.
 
 ### Installing all packages
 
@@ -102,6 +104,10 @@ From inside of VSCode, open the `launch.json` file and in the _Launch Integratio
 1. Double-check the `CHANGELOG.md` contains all desired change comments and has the version to be released with date at the top.
     * Go through all recent PRs and make sure they are properly accounted for.
     * Make sure all changelog entries have links back to their PR(s) if appropriate.
+1. Double-check that the node version we're using matches the one used for VS Code. If it doesn't, you will then need to update the node version in the following files:
+    * `.nvmrc` - this will enable `nvm` to automatically switch to the correct node version when you're in the project folder
+    * `.github/workflows/main.yml` - all the "node-version: <version>" settings
+    * `.github/workflows/release.yml` - the "node-version: <version>" setting
 1. Double-check that the extension `package.json` and `package-lock.json` have the version you intend to release. If you are doing a patch release (as opposed to minor or major version) this should already be correct.
 1. Create a PR for this release:
     * This PR will contain any missing bits from steps 1 and 2. Most of the time, this will just be updating `CHANGELOG.md` with today's date.

extensions/ql-vscode/.nvmrc

@@ -0,0 +1 @@
+v16.13.0