ardupilotmega: update OBSTACLE_DISTANCE_3D message

[rishabsingh3003]

This PR fixes some of the errors I had made before while making the message.
Also, I have added a new "orientation" field to the message. It makes it easier for the user to set up a camera that is not facing the centre. I'll do a follow-up PR inside our proximity library to add support for this field.

[peterbarker]

Kind of dubious removing the wip while also adding a field :-)

Fair illustration of where we need a separate message for describing the sensor vs supplying the data.

We really should have

<message id="11037" name="OBSTACLE_SENSOR_3D">
      <field type="uint32_t" name="time_boot_ms" units="ms">Timestamp (time since system boot).</field>
      <field type="uint8_t" name="sensor_id">Sensor id of the distance sensor.</field>
      <field type="uint8_t" name="sensor_type" enum="MAV_DISTANCE_SENSOR">Class id of the distance sensor type.</field>
      <field type="uint8_t" name="frame" enum="MAV_FRAME">Coordinate frame of reference.</field>
      <field type="uint8_t" name="orientation" enum="MAV_SENSOR_ORIENTATION">Direction the sensor faces. downward-facing: ROTATION_PITCH_270, upward-facing: ROTATION_PITCH_90, backward-facing: ROTATION_PITCH_180, forward-facing: ROTATION_NONE, left-facing: ROTATION_YAW_90, right-facing: ROTATION_YAW_270</field>
      <field type="float" name="min_distance" units="m">Minimum distance the sensor can measure.</field>
      <field type="float" name="max_distance" units="m">Maximum distance the sensor can measure.</field>
</message>

and then

     <message id="11038" name="OBSTACLE_DISTANCE_3D">
     <description>Obstacle located as a 3D vector.</description>
      <field type="uint32_t" name="time_boot_ms" units="ms">Timestamp (time since system boot).</field>
      <field type="uint8_t" name="sensor_id">Sensor id of the distance sensor.</field>
      <field type="uint16_t" name="obstacle_id" instance="true">Unique ID given to each obstacle so that its movement can be tracked. Use UINT16_MAX if object ID is unknown or cannot be determined.</field>
      <field type="float" name="x" units="m">X position of the obstacle.</field>
      <field type="float" name="y" units="m">Y position of the obstacle.</field>
      <field type="float" name="z" units="m">Z position of the obstacle.</field>
     </message>

We'd be sending 19 bytes of payload rather than 29. Ship has probably sailed on this, however, as there's too much GCS support that would need to be fixed before we get Copter out the door.

[peterbarker]

Perhaps this should go up next to MAV_FRAME?

We also need to clarify how orientation interacts with MAV_FRAME. Which is probably, "we ignore all but FRD so orientation is always vs FRD".

[rmackay9]

Should we specify here which frames we support? isn't that a bit too AP specific? or even AP Version specific?

[peterbarker]

@rishabsingh3003 what's your intent with this? Its getting very, very late to try to get this into the next Copter stable!

Once it's gone out in Copter-stable we're not going to be able to do anything except add extension fields.

[rmackay9]

I think removing the WIP label at least is a good idea and won't affect the format of the message so consumers will be unaffected as well.