Add to VSCode's recommended extensions (#6656)

This includes a number of recommended extensions from the VS Code doc page that should make coding things a lot easier for QMK Firmware.

.vscode/extensions.json

@@ -1,6 +1,11 @@
 // Suggested extensions
 {
   "recommendations": [
-    "EditorConfig.EditorConfig"
+    "EditorConfig.EditorConfig",
+    "xaver.clang-format",
+    "ms-vscode.cpptools",
+    "bierner.github-markdown-preview",
+    "donjayamanne.git-extension-pack",
+    "CoenraadS.bracket-pair-colorizer-2"
   ]
 }