feat: render semantic glass backdrops

compositor/src/state.rs

@@ -123,6 +123,7 @@ pub struct Ferese {
     pub(crate) window_shadows: HashMap<WindowId, crate::winit::WindowShadowBuffers>,
     pub(crate) rounded_clip_programs: HashMap<ErasedContextId, crate::winit::RoundedClipPrograms>,
     pub(crate) material_programs: HashMap<ErasedContextId, crate::winit::MaterialProgram>,
+    pub(crate) backdrop_programs: HashMap<ErasedContextId, crate::winit::BackdropProgram>,
     pub(crate) material_buffers: HashMap<WlSurface, crate::winit::MaterialBuffers>,
     material_scene_generation: u64,
     closing_windows: HashMap<WindowId, ClosingAnimation>,
@@ -438,6 +439,7 @@ impl Ferese {
             window_shadows: HashMap::new(),
             rounded_clip_programs: HashMap::new(),
             material_programs: HashMap::new(),
+            backdrop_programs: HashMap::new(),
             material_buffers: HashMap::new(),
             material_scene_generation: 0,
             closing_windows: HashMap::new(),