FlightMap: Fix drawing of very long mission lines

[rubenp02]

FlightMap: Fix drawing of very long mission lines

Description

This fixes a bug where extremely long legs in flight plans were drawn as straight lines on the map, instead of following the great circle path.

Key changes:

• Break down mission legs longer than 50km into smaller segments that follow the great circle path based on accurate geodesic calculations.
• Update leg arrow heading calculation to account for changing bearing along great circle paths.

Before/after

Checklist:

• [x] Review Contribution Guidelines.
• [x] Review Code of Conduct.
• [x] I have tested my changes.

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