Style is inconsistent within the Shader docs pages

[tetrapod00]

Your Godot version: 4.3 Issue description: Already working on a PR for this one.

Within the shader reference pages, there is some inconsistency in styling/markup. Built-in variables are styled as:

• VERTEX
• VERTEX
• VERTEX

Render modes are styled as:

• render_mode ``unshaded`
• the world_vertex_coords render mode

At least within these 5 pages, the style should be generally standardized.

URL to the documentation page (if already existing): https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/spatial_shader.html https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/canvas_item_shader.html https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/sky_shader.html https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/particle_shader.html https://docs.godotengine.org/en/latest/tutorials/shaders/shader_reference/fog_shader.html