ci: Add action for automatically running Prettier (#3727)

* ci: Add action for automatically running Prettier

This patch sets up a GitHub Action for automatically running Prettier. Now that #3725 has landed, automatically running Prettier shouldn't [generate too much noise](#3631 (comment)).

This will prevent needing to spend time opening PRs just for running Prettier, and enables us to remove some of the Grunt code for doing so.

* an unpretty change

* Prettified Code!

Co-authored-by: stephenmathieson <stephenmathieson@users.noreply.github.com>

.github/workflows/format.yml

@@ -0,0 +1,17 @@
+name: Formatter
+
+on: [pull_request]
+
+jobs:
+  prettier:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cloning the repository
+        uses: actions/checkout@v3
+        with:
+          ref: ${{ github.head_ref }}
+          fetch-depth: 0
+      - name: Prettify the code
+        uses: creyD/prettier_action@v4.2
+        with:
+          prettier_options: '--write .'