[3D] Add extrusion support

[MidnightCoder-m]

🚀 Description

Adds optional polygon extrusion to the 3D feature selection highlight. When a selected polygon's layer carries a height attribute, the highlight is rendered as a volumetric solid (vertical walls + a roof cap) instead of a flat fill, with
the height taken per-feature from that attribute.

✨ Key Changes

• Quick3DGeometryUtils: add generatePolygonWalls().
• Quick3DGeometry: new extrusionHeight property.
• MultiFeatureListModel / LayerUtils : new extrusionHeight model role, backed by LayerUtils::guessFriendlyHeightField().

ℹ️ How the extrusion height is determined

LayerUtils::guessFriendlyHeightField() scans the layer's numeric fields for a name matching candidate list (extrusion, height). The model role returns that field's value for each feature. When no suitable field exists it returns 0, so polygons keep rendering flat exactly as before.

🐛 A bug Fix: Terrain sampling (independent fix in this branch)

Quick3DTerrainProvider now rejects gross low DEM outliers: extreme low samples are marked as missing so isolated DEMspikes no longer drag down the computed height range.

Demo

Screencast.From.2026-06-24.20-37-40.mp4

[qfield-fairy]

🍎 MacOS DMG universal builds

Download a MacOS DMG universal build of this PR for testing.
(Built from commit 6c73111)

📱 Android builds

Download an Android arm64 build of this PR for testing.
(Built from commit 6c73111)

Other Android architectures

• arm-neon
• x64
• x86
• all access arm64
• all access arm-neon
• all access x64
• all access x86

🪟 Windows builds

Download a Windows build of this PR for testing and for arm64.

(Built from commit 6c73111)

🐧 Linux AppImage builds

Download a Linux AppImage build of this PR for testing.
(Built from commit 6c73111)

[beanzmo]

my first commit :)