AK: Rename adopt() to adopt_ref()

This makes it more symmetrical with adopt_own() (which is used to
create a NonnullOwnPtr from the result of a naked new.)

Userland/Libraries/LibWeb/CSS/Screen.h

@@ -21,7 +21,7 @@ public:
 
     static NonnullRefPtr<Screen> create(DOM::Window& window)
     {
-        return adopt(*new Screen(window));
+        return adopt_ref(*new Screen(window));
     }
 
     i32 width() const { return screen_rect().width(); }