[MAPS3D-2186] Promote elevated lines properties to stable: line-z-offset and line-elevation-reference (#9756)

Closes [MAPS3D-2186](https://mapbox.atlassian.net/browse/MAPS3D-2186)

This PR removes the experimental flag from the elevated lines properties
`line-z-offset` and `line-elevation-reference`. The property
`line-cross-slope` will remain experimental for now, as we might still
want to change how it works in the future.

[MAPS3D-2186]:
https://mapbox.atlassian.net/browse/MAPS3D-2186?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

```
<public>
Promote elevated lines properties to stable: `line-z-offset` and `line-elevation-reference` (#9756)
</public>
```

cc @mapbox/gl-js
cc @mapbox/maps-ios
cc @mapbox/sdk-platform
cc @mapbox/maps-android

GitOrigin-RevId: 9bfbd8e6d1d80e0787c4015b19537e3379cc0bc1

Author: lasselammi

CHANGELOG.md

@@ -3,12 +3,13 @@
 Mapbox welcomes participation and contributions from everyone.
 
 ## main
+* Introduce new `LineLayer.lineElevationGroundScale` property to scale elevated lines with terrain exaggeration.
+* Promote elevated lines properties to stable: `LineLayer.lineZOffset` and `LineLayer.lineElevationReference`.
 
 ## 11.19.0-beta.1 - 28 January, 2026
 
 ### 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.