Camera: CAMERA_FOV_STATUS always sent and attitude is earth-frame

[rmackay9]

This makes two improvements to the CAMERA_FOV_STATUS message sent to the GCS:

1. the message is always sent even the gimbal is pointing upwards meaning the image location cannot be calculated
2. the camera's attitude is sent in earth-frame resolving issue AP_Camera: FOV quaternion should be Earth-Frame #28113

This has been lightly tested in SITL. I'm quite confident that the first enhancement is all correct and below are some screen shots

I tested the 2nd change using printf debug and it seemed correct but SITL's gimbal simulator is a simple servo gimbal and reports even its roll and pitch in body-frame which made debugging slightly difficult. So I'd like @robertlong13 to confirm he's happy.

[robertlong13]

Looks good to me. Tested the quaternion output with my gimbal video testbed. I also validated that your math returns identical results to the dirty workaround I posted in my issue ticket:

mount->get_attitude_euler(get_mount_instance(), roll, pitch, yaw);
quat.from_euler(radians(roll), radians(pitch), radians(yaw) + AP::ahrs().get_yaw());