[MAPSPERF-51][GL-JS] Elevated raster layer: raster-elevation-reference support (#9490)

Fixes and improvements to elevated raster layers as requested by TWC.
Addresses: MAPSPERF-50 and MAPSPERF-51

**Context**

TWC reported
([RICO-15889](https://mapbox.atlassian.net/browse/RICO-15889))
inconsistent shading for raster layers when switching between mercator
and globe projections.
Maintaining uniform shading is technically unfeasible for draped or
baked raster layers across mercator/globe projection.
Idea to work around this limitation, is to move layers out of the
draping using raster-elevation to get consistent shading of the layer
even during mercator/globe transitions.

In order to also support terrain (and not intersect with terrain
geometry), this PR introduces `raster-elevation-reference:
{ground,sea}`, enabling the layer to follow the terrain surface
(`ground`) or maintain constant elevation above sea level (`sea` -
default) while applying z-bias to resolve depth-testing conflicts.

**Demo**:
https://labs.tilestream.net/labs-raster-layer/raster-elevation.htm

> [!NOTE]
> Implementation is for GL-JS only, changes in native are result of
shader changes.
> Native implementation will follow in separate PR.

**Changes**
- Add z-bias to fix z-fighting for raster layers independent of
elevation
- Add new **experimental** paint property `raster-elevation-reference`
to apply elevation relative to ground or sea (default) level
- Render test `raster-elevation-tiled/terrain-ground-reference` (gl-js
only, disabled in native)

**How does it look?**

https://github.com/user-attachments/assets/a9463bab-b460-4e6e-991a-289e03b576e0

Style config:
~~~json
{
            "id": "image",
            "type": "raster",
            "source": "twc-raster-elevation",
            "slot": "middle",
            "paint": {
                "raster-fade-duration": 0,
                "raster-opacity": 0.5,
                "raster-elevation": 0.0001,
                 "raster-elevation-reference": "ground"
                "raster-emissive-strength": 1.0
            }
        }
~~~

~~~
<public>
Fix z-fighting for elevated raster layers.
Add paint property raster-elevation-reference to elevate raster layers
relative to ground instead of sea level.
</public>
~~~

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

[RICO-15889]:
https://mapbox.atlassian.net/browse/RICO-15889?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

---------

Co-authored-by: Aleksandar Stojiljković <aleksandar.stojiljkovic@mapbox.com>
GitOrigin-RevId: 8c8269d43c23ddc0647b26184123baa010556359

Author: 2 people