fix: parse dawnToggles properly

[pepperoni505]

This is a follow-up to #374. I seem to have forgotten to push this commit, which is required to actually parse the property. Sorry about that!

[wcandillon]

Thanks for doing this. Now we didn't catch this ealier because we didn't try any valid toggles. Could you add the following test if sensible:

diff --git a/packages/webgpu/src/__tests__/DawnToggles.spec.ts b/packages/webgpu/src/__tests__/DawnToggles.spec.ts
index 574a985..96900ac 100644
--- a/packages/webgpu/src/__tests__/DawnToggles.spec.ts
+++ b/packages/webgpu/src/__tests__/DawnToggles.spec.ts
@@ -38,4 +38,59 @@ describe("Dawn toggles", () => {
     });
     expect(result).toBe(true);
   });
+
+  // The tests above only assert that requestDevice resolves, which is true
+  // whether or not the toggle is parsed and chained onto the device descriptor.
+  // This test instead activates a real toggle (skip_validation) and observes a
+  // behavioral difference, so it fails if dawnToggles ever stops being applied.
+  it("applies skip_validation so a normally-invalid buffer creates without error", async () => {
+    // dawnToggles is a non-standard Dawn extension; browsers ignore it, so the
+    // behavioral difference only exists on the native (Dawn) backends.
+    if (client.OS === "web") {
+      return;
+    }
+    const result = await client.eval(({ gpu }) => {
+      // MAP_READ may only be combined with COPY_DST and MAP_WRITE only with
+      // COPY_SRC, so MAP_READ | MAP_WRITE is a validation error by default. The
+      // buffer is never used on the GPU, so creating it with validation skipped
+      // is harmless on every backend.
+      const invalid = {
+        size: 16,
+        usage: GPUBufferUsage.MAP_READ | GPUBufferUsage.MAP_WRITE,
+      };
+      // A fresh adapter per device: an adapter only vends a single device.
+      return gpu
+        .requestAdapter()
+        .then((adapter) => adapter!.requestDevice())
+        .then((control) => {
+          control.pushErrorScope("validation");
+          control.createBuffer(invalid);
+          return control.popErrorScope();
+        })
+        .then((controlError) =>
+          gpu
+            .requestAdapter()
+            .then((adapter) =>
+              adapter!.requestDevice({
+                dawnToggles: { enabledToggles: ["skip_validation"] },
+              }),
+            )
+            .then((toggled) => {
+              toggled.pushErrorScope("validation");
+              toggled.createBuffer(invalid);
+              return toggled.popErrorScope();
+            })
+            .then((toggledError) => ({
+              controlHadError: controlError !== null,
+              toggledHadError: toggledError !== null,
+            })),
+        );
+    });
+    // The operation is genuinely invalid on this build (guards against the test
+    // silently passing because the buffer became valid).
+    expect(result.controlHadError).toBe(true);
+    // skip_validation took effect, which is only possible if dawnToggles was
+    // parsed and chained onto the device descriptor.
+    expect(result.toggledHadError).toBe(false);
+  });
 });

[pepperoni505]

Done, thank you!