SkyController: refactoring, new simple sky mode, improvements and bug fixes

[airnez]

Description

This PR has to be merged after #2699. It is its follow-up. It answers some of the issues pointed out by #2780.

Major changes

It introduces a new architecture for sky management:

Sky strategies

• SkyManager code was mostly moved into RealisticSky. It implements the new interface ISkyStrategy.
• A new "simple" sky mode was introduced with SimpleSky. It also implements ISkyStrategy. It changes the sky color based on altitude, adds fog to the scene and renders an "atmospheric gradient" to blend the fog with the sky. A skyAltitude parameter defines when the sky changes color. Fog and horizon gradient are disabled above this value, and their spread is increased when getting closer to the ground.
• The HorizonGradient code and its shader hold responsability for the atmospheric gradient rendering. It's a full-screen quad rendered on a Mesh. This part was mostly written with LLMs.
• A new SkyController was created to handle sky-related logic away from the view. It was named so to avoid confusions with SkyManager that was also renamed. It lazy-loads sky strategies, preventing from initializing three-geospatial when not required.
• Providing an API to modify atmosphere parameters (see mars example)
• Actually removing RealisticSky effect passes from the composer when disabling it. The realisticLighting mode was still having effects on the view when disabled.

SunLight and shadow casting

• Adding a new forceDaytime option to the sunLightLayer to make the sun "follow" the camera instead of relying on a Date. The sun is aligned with the camera to display the full globe, and tilts when zooming in to cast shadows nicely.
• Computing the shadows box size based on distance to the sun target instead of using camera far.
• Turning off shadow casting above a shadowsMaxAltitude parameter
• Making the "sun intensity hack" that prevents from lighting buildings from below when the sun is behing horizon only apply when close to the ground, under shadowsMaxAltitude parameter

Minor changes

• Making the 3DTiles meshes matte
• Disabling any sky effect during debug camera render for consistency
• Tweeking realistic lighting Aerial Perspective Blending to make it look better

Notes

• For now, Realistic lighting is not compatible with dynamic far. Many more tiles are displayed when it is enabled.

Screenshots

Globe appearance improvements (this branch versus master)

Simple Sky

forceDayTime

Matte 3D tiles mesh

Adjusting aerial perspective blending (this branch versus master)

Mars simple and realistic atmosphere

Debug camera render ignores the sky effects

[airnez]

@Desplandis rebased on master and pushed 4 new commits:

• Set a smaller default sse for 3dtiles loader example
• Disable realisticLigthing by default for 3dtiles loader example
• Add an ambient light when sunlightLayer is off in SkyController
• Provide an uniform realistic lighting debug ui