ci: Build and publish system extensions

Use gnomeos-build-sysext CI/CD component to build a system extension
for gnome-shell. This is part of on-going efforts discussed here [1].

[1] https://discourse.gnome.org/t/towards-a-better-way-to-hack-and-test-your-system-components/21075

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3390>

.gitlab-ci.yml

@@ -4,6 +4,15 @@ include:
   - remote: 'https://gitlab.freedesktop.org/freedesktop/ci-templates/-/raw/bc70242ffb8402243e934659ecc1a2d1c89eca2b/templates/ci-fairy.yml'
   - project: 'Infrastructure/openshift-images/gnome-release-service'
     file: '/ci-templates/release-module.yml'
+  - component: gitlab.gnome.org/GNOME/citemplates/gnomeos-build-sysext@1.0.0-alpha
+    inputs:
+      meson-options:
+        -Dextensions_app=false
+        -Dextensions-tool:bash_completion=disabled
+
+build-sysext:
+  before_script:
+    - .gitlab-ci/install-gnomeos-sysext-dependencies.sh $CI_PROJECT_DIR/extension
 
 stages:
   - pre_review

.gitlab-ci/install-gnomeos-sysext-dependencies.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+#
+# This script ensures that all dependencies required to build and run
+# a GNOME Shell system extension are present in:
+#
+# The building environment, by installing these dependencies to the container.
+# The running environment, by bundling these dependencies with the extension.
+#
+
+set -e
+
+# Install dependencies to $SYSEXT_DEST_DIR to bundle these with the extension.
+
+SYSEXT_DEST_DIR="$(realpath $1)"
+
+# Ensure that we're building against (and bundling) the right mutter branch
+# and its dependencies:
+
+SCRIPT_DIR="$(dirname $0)"
+
+$SCRIPT_DIR/checkout-mutter.sh
+./mutter/.gitlab-ci/install-gnomeos-sysext-dependencies.sh $SYSEXT_DEST_DIR
+
+meson setup mutter/build mutter --prefix=/usr --libdir="lib/$(gcc -print-multiarch)"
+meson compile -C mutter/build
+meson install -C mutter/build --destdir $SYSEXT_DEST_DIR
+
+sudo meson install -C mutter/build
+
+# Ensure that any other dependency missing in GNOME OS is installed and bundled
+# here as it was done with mutter: