Add a section about coordinate spaces to shader pages.

[tetrapod00]

Resolves https://github.com/godotengine/godot-docs/issues/9780.

This PR aims to add a list of coordinate spaces to various shader pages:

• Spatial shaders will have a section with a table and some conversion snippets.
• CanvasItem shaders will have a section with a table and some conversion snippets.
• Particle shaders will link to Spatial and CanvasItem sections.
• Fog and Sky could either link to Spatial, copy the entire section, or only list the world spaces they use.