Auto merge of #12178 - frewsxcv:prefs, r=emilio

Refactor `util::prefs` operations to be methods on static struct.

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components/style/properties/longhand/box.mako.rs

@@ -58,7 +58,7 @@
             % for value in values:
                 "${value}" => {
                     % if value in experimental_values:
-                        if !::util::prefs::get_pref("layout.${value}.enabled")
+                        if !::util::prefs::PREFS.get("layout.${value}.enabled")
                             .as_boolean().unwrap_or(false) {
                             return Err(())
                         }