chore: add global prettier ignore file

As prettier is not configured for this project, and the style doesn't
meet prettier's opinionated defaults, it's worth dropping this blanket
ignore until such a time (if ever) a prettier config is produced that
matches the styleguide of this project.

.vscode/extensions.json

@@ -0,0 +1,5 @@
+{
+	"recommendations": [
+		"editorconfig.editorconfig"
+	]
+}