feat(unstable/webgpu): add deviceStartCapture and deviceStopCapture (#28192)

This is achieved by adding a new `Deno.webgpu` namespace which will be
used for non-spec functionality, which for now will be marked as
unstable

cli/tsc/dts/lib.deno.unstable.d.ts

@@ -4399,6 +4399,40 @@ declare namespace Deno {
     export {}; // only export exports
   }
 
+  /**
+   * The webgpu namespace provides additional APIs that the WebGPU specification
+   * does not specify.
+   *
+   * @category GPU
+   * @experimental
+   */
+  export namespace webgpu {
+    /**
+     * Starts a frame capture.
+     *
+     * This API is useful for debugging issues related to graphics, and makes
+     * the captured data available to RenderDoc or XCode
+     * (or other software for debugging frames)
+     *
+     * @category GPU
+     * @experimental
+     */
+    export function deviceStartCapture(device: GPUDevice): void;
+    /**
+     * Stops a frame capture.
+     *
+     * This API is useful for debugging issues related to graphics, and makes
+     * the captured data available to RenderDoc or XCode
+     * (or other software for debugging frames)
+     *
+     * @category GPU
+     * @experimental
+     */
+    export function deviceStopCapture(device: GPUDevice): void;
+
+    export {}; // only export exports
+  }
+
   export {}; // only export exports
 }