build: Pass library as first argument to pkg.generate()

Dependencies are added automatically, and we no longer get warnings
like:

clutter/clutter/meson.build:628: DEPRECATION: Library mutter-clutter-4
was passed to the "libraries" keyword argument of a previous call to
generate() method instead of first positional argument. Adding
mutter-clutter-4 to "Requires" field, but this is a deprecated behaviour
that will change in a future version of Meson. Please report the issue
if this warning cannot be avoided in your case.

src/meson.build

@@ -833,11 +833,10 @@ if have_introspection
   )
 endif
 
-pkg.generate(
+pkg.generate(libmutter,
   name: 'Meta',
   filebase: 'libmutter-' + libmutter_api_version,
   description: 'Mutter compositor and window manager library',
-  libraries: [libmutter],
   subdirs: pkgname,
   requires: [mutter_pkg_deps, libmutter_clutter_name],
   version: meson.project_version(),