Update to use OpenCV 4.11.0 and JavaCPP 1.5.12.

This removes a warning on launch about JavaCPP versions being inconsistent (caused by TensorFlow pulling in a more recent JavaCPP version than we were using for OpenCV).

Also, remove use of `Gson.setLenient()` to remove more startup warnings.

Finally, update `QP.getCurrentServer()` to return `ImageServer<BufferedImage>` instead of `ImageServer<?>`. This didn't cause warnings on startup, but it could cause annoyances when trying to write scripts in an IDE.

This was failing on Windows, but passing on macOS.

The OpenCV docs suggest that meanStdDev should not be used for more than 4 channels; that didn't appear to be related to the problem that caused the failing tests, but now we extract channels anyway to try to ensure the results are reliable.