MAVLink Inspector: Add back Instance Awareness

[hamishwillee]

MAVLink messages that have an "instance field" should support separate plotting and reporting for each value of the instance field.

As an example consider the BATTERY_STATUS message. This has the id field with the instance="true" attribute as shown below:

<field type="uint8_t" name="id" instance="true">Battery ID</field>

If a vehicle has multiple batteries then each of these should have a different value for id and should be plotted separately. As it is now a plot of BATTERY_STATUS is useless for multi-battery systems, because the message plot shows traces that switch between different sources.

Currently this affects batteries, ESC, IMUs, but there are others, and more to come.

Note that this was previously supported, but was lost when transitioning to QML controls.

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Tell us a bit about the feature:

• What problem does it solve?

  Allows instance data to be plotted and inspected.

• What does it do?

  Allows data to be presented usefully

• What flight stacks must it work with? (All, PX4, ArduPilot)

  All

• Relevant vehicle types? (All, multirotor, fixed-wing, VTOL, submarine, etc.)

  All

• Are there other systems that have this feature?

  Mission Planner.

• What communication/integration standards does the feature rely on (e.g. MAVLink commands etc.)

  MAVLink

[DronecodeBot]

This issue has been mentioned on Discussion Forum for PX4, Pixhawk, QGroundControl, MAVSDK, MAVLink. There might be relevant details there:

https://discuss.px4.io/t/custom-mavlink-messages-for-multiple-instances/42597/21