Blade window transparency (#10973)

Release Notes:

- N/A

Following up to #10880
TODO:
- [x] create window as transparent
  - [x] X11
  - [x] Wayland
  - [ ] Windows
  - [x] MacOS (when used with Blade)  
- [x] enable GPU surface transparency
- [x] adjust the pipeline blend modes
- [x] adjust shader outputs


![transparency2](https://github.com/zed-industries/zed/assets/107301/d554a41b-5d3f-4420-a857-c64c1747c2d5)

Blurred results from @jansol (on Wayland), who contributed to this work:


![zed-blur](https://github.com/zed-industries/zed/assets/107301/a6822171-2dcf-4109-be55-b75557c586de)

---------

Co-authored-by: Jan Solanti <jhs@psonet.com>

crates/gpui/src/platform/mac/metal_renderer.rs

@@ -37,6 +37,7 @@ pub unsafe fn new_renderer(
     _native_window: *mut c_void,
     _native_view: *mut c_void,
     _bounds: crate::Size<f32>,
+    _transparent: bool,
 ) -> Renderer {
     MetalRenderer::new(context)
 }
@@ -231,6 +232,10 @@ impl MetalRenderer {
         }
     }
 
+    pub fn update_transparency(&mut self, _transparent: bool) {
+        // todo(mac)?
+    }
+
     pub fn destroy(&mut self) {
         // nothing to do
     }

crates/gpui/src/platform/mac/window.rs

@@ -626,6 +626,7 @@ impl MacWindow {
                     native_window as *mut _,
                     native_view as *mut _,
                     window_size,
+                    window_background != WindowBackgroundAppearance::Opaque,
                 ),
                 request_frame_callback: None,
                 event_callback: None,
@@ -979,7 +980,10 @@ impl PlatformWindow for MacWindow {
     fn set_app_id(&mut self, _app_id: &str) {}
 
     fn set_background_appearance(&mut self, background_appearance: WindowBackgroundAppearance) {
-        let this = self.0.as_ref().lock();
+        let mut this = self.0.as_ref().lock();
+        this.renderer
+            .update_transparency(background_appearance != WindowBackgroundAppearance::Opaque);
+
         let blur_radius = if background_appearance == WindowBackgroundAppearance::Blurred {
             80
         } else {