[MAPS3D-2179] Add new line-elevation-ground-scale property to scale elevated lines with terrain exaggeration (#9440)

Closes https://mapbox.atlassian.net/browse/MAPS3D-2179

This PR adds a new layout property `line-elevation-ground-scale`, which
allows scaling line elevation data with terrain exaggeration for lines
that use `line-elevation-reference: "sea"`. Previously such lines were
always rendered at the exact elevation provided by the source data while
ignoring the terrain exaggeration value. This worked correctly as long
as terrain exaggeration was `1`. Disabling terrain by transitioning
terrain elevation to `0` would cause the elevated line to lose any
connection it had with the ground. Here's an example:

https://github.com/user-attachments/assets/a1b7e691-d850-491c-81e0-a7473810b765

With the new property it's possible to scale elevation values with
terrain exaggeration, either for the entire length of the line or for
parts of it only. For flight paths good results can be had by
interpolating at the start and end of the line. Here is an example of
using the property to keep the start and end of the flight path
connected with the ground:
```
"line-elevation-ground-scale": [
    "interpolate",
    [
        "linear"
    ],
    [
        "line-progress"
    ],
    0,
    1,
    0.1,
    0,
    0.9,
    0,
    1,
    1
]
```

https://github.com/user-attachments/assets/92485a5c-b974-45e3-b0bb-67f1c38df68f

```
<public>
Add `line-elevation-ground-scale` property to scale elevated lines with terrain exaggeration (#9440)
</public>
```

cc @mapbox/gl-js
cc @mapbox/gl-native
cc @mapbox/maps-ios
cc @mapbox/maps-android

cc @mapbox/sdk-platform

---------

Co-authored-by: Changelog autocreator bot <actions@github.com>
(cherry picked from commit 5513c0747c841d28a588be8c8441d9fa0339f1fd)
GitOrigin-RevId: 5166ab994955594b95841554951496617f7957ac

Author: 2 people

CHANGELOG.md

@@ -8,6 +8,11 @@ Mapbox welcomes participation and contributions from everyone.
 
 ### Features ✨ and improvements 🏁
 * Introduce experimental `queryRenderedRasterValues` API for querying the rendered raster array value at a point on the map.
+* Introduce new `LineLayer.lineElevationGroundScale` property to scale elevated lines with terrain exaggeration.
+
+### Bug fixes 🐞
+* Fix `FrameViewAnnotationsExample` annotations disappearing before shadow leaves the screen.
+
 ## 11.18.0 - 15 January, 2026
 
 ### Bug fixes 🐞