CI now uses actions/setup-node to setup Node and restore the Yarn cache (#89363)

## About The Pull Request
This PR changes CI to use `actions/setup-node` to setup Node, instead of
using `tools/ci/install_node.sh`. The version given to this action is
the same as specified in `dependencies.sh`.

This fixes the issue of CI not using the node version provided in
`dependencies.sh`. Previously, it was using the system-wide Node, which
at the time of this PR is `v20.18.2`.

This change is NOT applied across all jobs, but is applied at minimum to
any jobs where the game is compiled. For example, any integration test
jobs now use `actions/setup-node` - but the "Remove guide comments" job
is untouched.

This PR has the additional following effects:
* The node install is no longer cached - it is instead downloaded from
<https://github.com/actions/node-versions> (or
<https://nodejs.org/dist/> if that fails). Being that the CI runner
needs to contact Github anyways to obtain the cached Node install, this
should make no difference.
* We no longer have to perform Yarn caching ourselves -
`actions/setup-node` does it for us! However, a side effect of this is
that the Yarn cache uses a different cache key now. I would have set up
the action to pull from the existing cache, but unfortunately that
wasn't an option.

Speaking of caching - the new action, `.github/actions/setup_node`, will
NOT restore the Yarn cache unless the `restore-yarn-cache` input is
`true`. This saves a couple seconds where we need node, but don't need
the yarn cache (such as in integration tests).

.github/actions/setup_node/action.yml

@@ -0,0 +1,26 @@
+# This action is a wrapper around `actions/setup-node`, to use the version specified in
+# `dependencies.sh`.
+name: Setup Node
+description: Install Node using the version specified in `dependencies.sh`; additionally, restores the Yarn cache if one exists
+
+inputs:
+  restore-yarn-cache:
+    description: 'If `true`, restores the Yarn cache alongside installing node.'
+    required: false
+    type: boolean
+    default: false
+
+runs:
+  using: composite
+  steps:
+    - name: Configure Node version
+      shell: bash
+      run: |
+        source dependencies.sh
+        echo "NODE_VERSION_REQUIRED=$NODE_VERSION_LTS" >> $GITHUB_ENV
+    - name: Install Node
+      uses: actions/setup-node@v4
+      with:
+        node-version: ${{ env.NODE_VERSION_REQUIRED }}
+        cache: ${{ fromJSON(inputs.restore-yarn-cache) && 'yarn' || '' }}
+        cache-dependency-path: ${{ fromJSON(inputs.restore-yarn-cache) && 'tgui/yarn.lock' || '' }}