deno_webgpu: Select wgpu backends based on target.

This used to be managed by wgpu-core, but now must be handled by
wgpu-core's users - like this crate.

deno_webgpu/Cargo.toml

@@ -14,5 +14,23 @@ description = "WebGPU implementation for Deno"
 deno_core.workspace = true
 serde = { workspace = true, features = ["derive"] }
 tokio = { workspace = true, features = ["full"] }
-wgpu-core = { workspace = true, features = ["trace", "replay", "serde", "strict_asserts", "wgsl"] }
 wgpu-types = { workspace = true, features = ["trace", "replay", "serde"] }
+
+[dependencies.wgpu-core]
+workspace = true
+features = ["trace", "replay", "serde", "strict_asserts", "wgsl", "gles"]
+
+# We want the wgpu-core Metal backend on macOS and iOS.
+[target.'cfg(any(target_os = "macos", target_os = "ios"))'.dependencies.wgpu-core]
+workspace = true
+features = ["metal"]
+
+# We want the wgpu-core Direct3D backends on Windows.
+[target.'cfg(windows)'.dependencies.wgpu-core]
+workspace = true
+features = ["dx11", "dx12"]
+
+# We want the wgpu-core Vulkan backend on Unix (but not Emscripten) and Windows.
+[target.'cfg(any(windows, all(unix, not(target_arch = "emscripten"))))'.dependencies.wgpu-core]
+workspace = true
+features = ["vulkan"]