tools/create-toolbox: Allow skipping mutter build

The container is useless for building or running gnome-shell unless
it includes the correct mutter version, so building it by default
makes sense.

However a manual build can be significantly faster when there's an
existing build dir, so add an option to skip the automatic build.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2713>

tools/toolbox/create-toolbox.sh

@@ -18,6 +18,7 @@ usage() {
 	  -v, --version=VERSION   Create container for stable version VERSION
 	                          (like 44) instead of the main branch
 	  -r, --replace           Replace an existing container
+	  --skip-mutter           Do not build mutter
 	  -h, --help              Display this help
 
 	EOF
@@ -38,6 +39,7 @@ TEMP=$(getopt \
   --longoptions 'name:' \
   --longoptions 'version:' \
   --longoptions 'replace' \
+  --longoptions 'skip-mutter' \
   --longoptions 'help' \
   -- "$@")
 
@@ -63,6 +65,11 @@ while true; do
       shift
     ;;
 
+    --skip-mutter)
+      SKIP_MUTTER=1
+      shift
+    ;;
+
     -h|--help)
       usage
       exit 0
@@ -86,4 +93,4 @@ fi
 podman pull $TOOLBOX_IMAGE:$TAG
 
 toolbox create --image $TOOLBOX_IMAGE:$TAG $NAME
-toolbox_run update-mutter
+[[ $SKIP_MUTTER ]] || toolbox_run update-mutter