Add a complete description of TIME to Spatial, Particle, Sky, and Fog shaders.

[tetrapod00]

Your Godot version:
4.2, 4.3
Issue description:
The built-in global shader uniform TIME is fully documented for CanvasItem shaders, but not in Spatial, Particle, Sky, or Fog shaders.
Presumably this is the same global uniform for all shader types.

Proposal:
Copy the description from the CanvasItem shader page to the other pages.

URL to the documentation page (if already existing):
Documented here: https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/canvas_item_shader.html#global-built-ins
Incompletely documented here:

• https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/spatial_shader.html#global-built-ins
• https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/particle_shader.html#global-built-ins
• https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/sky_shader.html#global-built-ins
• https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/fog_shader.html#global-built-ins

[tetrapod00]

I'm working on a PR for this.