Captures the visible viewport of an initialized embedded native WebView as PNG data.
public Task<NativeWebViewSnapshot?> CaptureSnapshotAsync(CancellationToken cancellationToken = default(CancellationToken))
This operation is best-effort and returns null when the platform does not support
embedded snapshots, the control is uninitialized, or a native capture is temporarily unavailable or fails.
Cancellation is propagated to the caller.