[gnome-shell] build: Use meson's gnome.post_install()

[Marge Bot <marge-bot src gnome org>]

commit 00e5f40ddd5d2f31843306fded5c031f6b8db307
Author: Florian Müllner <fmuellner gnome org>
Date:   Wed Dec 22 20:11:31 2021 +0100

    build: Use meson's gnome.post_install()
    
    ... instead of the external script.
    
    Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2077>

 meson.build                                        |  6 ++++-
 meson/postinstall.py                               | 27 ----------------------
 .../extensions-app/build-aux/meson/postinstall.py  |  1 -
 subprojects/extensions-app/meson.build             |  4 +++-
 4 files changed, 8 insertions(+), 30 deletions(-)
---
diff --git a/meson.build b/meson.build
index 4b192847c7..470ea64321 100644
--- a/meson.build
+++ b/meson.build
@@ -295,7 +295,11 @@ if get_option('gtk_doc')
   subdir('docs/reference')
 endif
 
-meson.add_install_script('meson/postinstall.py')
+gnome.post_install(
+  glib_compile_schemas: true,
+  gtk_update_icon_cache: true
+)
+
 meson.add_dist_script('meson/generate-manpages.py')
 meson.add_dist_script('meson/generate-stylesheets.py')
 meson.add_dist_script('meson/check-version.py', meson.project_version(), 'NEWS')
diff --git a/subprojects/extensions-app/meson.build b/subprojects/extensions-app/meson.build
index 21dd448256..432ea1baaa 100644
--- a/subprojects/extensions-app/meson.build
+++ b/subprojects/extensions-app/meson.build
@@ -60,7 +60,9 @@ if not meson.is_subproject()
 
   subdir('po')
 
-  meson.add_install_script('build-aux/meson/postinstall.py')
+  gnome.post_install(
+    gtk_update_icon_cache: true
+  )
 
   if appstream_util.found()
     meson.add_dist_script('build-aux/meson/check-version.py',