Bug 1799901 - Enable panel animations on Linux configurations that support CSD. r=stransky

The problems we know about are about tiling WMs, this should work.

Depends on D161693

Differential Revision: https://phabricator.services.mozilla.com/D161694

widget/gtk/nsLookAndFeel.cpp

@@ -981,8 +981,8 @@ nsresult nsLookAndFeel::NativeGetInt(IntID aID, int32_t& aResult) {
       break;
     }
     case IntID::PanelAnimations:
-      // Disabled for now for issues in some configurations, see bug 1385079.
-      aResult = 0;
+      // Disabled on systems without CSD, see bug 1385079.
+      aResult = sCSDAvailable;
       break;
     case IntID::UseOverlayScrollbars: {
       aResult = StaticPrefs::widget_gtk_overlay_scrollbars_enabled();