Meta+Userland: Run the GML formatter on CI and pre-commit

Now that the GML formatter is both perserving comments and also mostly
agrees to the existing GML style, it can be used to auto-format all the
GML files in the system. This commit does not only contain the scripts
for running the formatting on CI and the pre-commit hook, but also
initially formats all the existing GML files so that the hook is
successfull.

Meta/lint-gml-format.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+set -e
+
+script_path=$(cd -P -- "$(dirname -- "$0")" && pwd -P)
+cd "${script_path}/.." || exit 1
+
+if [ -z "${GML_FORMAT:-}" ] ; then
+    if ! [ -d Build/lagom/ ] ; then
+        echo "Directory Build/lagom/ does not exist. Skipping GML formatting."
+        exit 0
+    fi
+    if ! [ -r Build/lagom/gml-format ] ; then
+        echo "Lagom executable gml-format was not built. Skipping GML formatting."
+        echo "To enable this check, you may need to run './Meta/serenity.sh build lagom' first."
+        exit 0
+    fi
+    GML_FORMAT="Build/lagom/gml-format"
+fi
+
+find AK Base Documentation Kernel Meta Ports Tests Userland -type f -name '*.gml' -print0 | xargs -0 "${GML_FORMAT}" -i