Add interactive 3D terrain extent panning and zooming

[mohsenD98]

🚀 Description

Adds interactive extent manipulation to the 3D terrain view, allowing users to pan and zoom the terrain in 3d mode.

✨ Key Changes

• Shift+Drag to pan extent — Hold Shift and drag to move the 3D terrain extent geographically. The terrain mesh translates in real-time for visual feedback, then regenerates at the new location on release.
• Shift+Wheel to zoom extent — Hold Shift and scroll to scale the terrain extent in/out around its center.
• setCustomExtent() API — New Q_INVOKABLE method on Quick3DTerrainProvider to programmatically set a custom geographic extent, with shared applyExtent() logic to avoid code duplication with updateFromMapSettings().
• 2D ↔ 3D extent sync — When closing the 3D view, the 2D map canvas extent is set to match the current 3D terrain extent.

Demo :)

Screencast.From.2026-02-24.21-59-10.mp4

[qfield-fairy]

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