gnome.compile_schemas() sets GSETTINGS_SCHEMA_DIR into devenv

When using gnome.compile_schemas() the location of the compiled schema is added to GSETTINGS_SCHEMA_DIR environment variable when using meson devenv command.

update_desktop_database added to gnome.post_install()

Applications that install a .desktop file containing a MimeType need to update the cache upon installation. Most applications do that using a custom script, but it can now be done by Meson directly.

See gnome.post_install().