Copter, AP_Mission: Send progress for individual mission items (take 2)

[nexton-winjeel]

Replaces #25249

This PR:

• adds the framework in AP_Mission for populating and transmitting the progress fields of a new NAV_CONTROLLER_PROGRESS message; and
• updates Copter to send this information for a variety of mission items.

Requires: ArduPilot/mavlink#366

[nexton-winjeel]

Example of what the GCS side looks like can be seen here: mavlink/mavlink#2029 (comment)

[nexton-winjeel]

Uses ~1232 bytes of flash (as tested on CubeOrange):

          Target          Text (B)  Data (B)  BSS (B)  Total Flash Used (B)  Free Flash (B)  External Flash Used (B)
          ----------------------------------------------------------------------------------------------------------
enabled:  bin/arducopter   1841556      3920   258372               1845476          120588  Not Applicable 
disabled: bin/arducopter   1840324      3920   258372               1844244          121820  Not Applicable