render: Disable wgpu unused shader output check when possible

Since wgpu hasn't yet released a version with this feature, I manually
backported it to the 0.17 branch.
This doesn't work on Windows (HLSL), but works on all other platforms.

Cargo.toml

@@ -82,3 +82,10 @@ inherits = "release"
 
 [profile.web-wasm-extensions]
 inherits = "release"
+
+# FIXME - remove this when wgpu v0.18 is released
+[patch.crates-io]
+wgpu = { git = "https://github.com/ruffle-rs/wgpu", branch = "backport-shader-unconsumed" }
+
+[patch.'https://github.com/gfx-rs/naga']
+naga = { version = "0.13.0" }

render/wgpu/src/backend.rs

@@ -1104,6 +1104,13 @@ async fn request_device(
         features |= wgpu::Features::TEXTURE_ADAPTER_SPECIFIC_FORMAT_FEATURES;
     }
 
+    if adapter
+        .features()
+        .contains(wgpu::Features::SHADER_UNUSED_VERTEX_OUTPUT)
+    {
+        features |= wgpu::Features::SHADER_UNUSED_VERTEX_OUTPUT;
+    }
+
     adapter
         .request_device(
             &wgpu::DeviceDescriptor {