[metal] expose render_layer (#8707)

Author: xiaopengli89

CHANGELOG.md

@@ -201,6 +201,7 @@ By @cwfitzgerald in [#8609](https://github.com/gfx-rs/wgpu/pull/8609).
 #### Metal
 
 - Add support for mesh shaders. By @SupaMaggie70Incorporated in [#8139](https://github.com/gfx-rs/wgpu/pull/8139)
+- Expose render layer. By @xiaopengli89 in [#8707](https://github.com/gfx-rs/wgpu/pull/8707)
 
 #### Naga
 

wgpu-hal/src/metal/surface.rs

@@ -50,6 +50,10 @@ impl super::Surface {
         Self::new(layer.to_owned())
     }
 
+    pub fn render_layer(&self) -> &Mutex<metal::MetalLayer> {
+        &self.render_layer
+    }
+
     /// Get or create a new `CAMetalLayer` associated with the given `NSView`
     /// or `UIView`.
     ///