Add workspace_overview_is_open function; put in a utils::quirks mod

This is increasingly not just related to screencopy, so it's weird to
add there. I don't see any other module that fits, so add one called
"quirks" (like the Linux kernel uses for device-specific handling in
generic drives).

src/backend/render/mod.rs

@@ -20,11 +20,11 @@ use crate::{
         CosmicMappedRenderElement, OverviewMode, SeatExt, SessionLock, Trigger, WorkspaceDelta,
         WorkspaceRenderElement,
     },
-    utils::prelude::*,
+    utils::{prelude::*, quirks::WORKSPACE_OVERVIEW_NAMESPACE},
     wayland::{
         handlers::{
             data_device::get_dnd_icon,
-            screencopy::{render_session, FrameHolder, SessionData, WORKSPACE_OVERVIEW_NAMESPACE},
+            screencopy::{render_session, FrameHolder, SessionData},
         },
         protocols::workspace::WorkspaceHandle,
     },