MAVExplorer: Add verbose output of DF log messages

[shancock884]

This PR provides the MAVExplorer side of: ArduPilot/pymavlink#911

It enables the use of the '--verbose' argument on the dump command for DF logs.
I use hasattr to check for dump_verbose function to avoid exception in case an older pymavlink is installed.

Example of output:

MAV> dump --verbose POS
2023-12-30 09:59:58.079: POS
    TimeUS: 37126810 µs
    Lat: 33.810313 deglatitude
    Lng: -118.393867 deglongitude
    Alt: -0.14000000059604645 m
    RelHomeAlt: -0.535001277923584 m
    RelOriginAlt: -0.21500125527381897 m

[peterbarker]

Merged, thanks!