Combine transparency limitation notes into section in 3D rendering limitations

[tetrapod00]

Your Godot version:

Issue description:
The 3D rendering limitations page already has a lengthy section on transparency sorting, but there are some other limitations of transparency that should be documented:

• All opaque objects render, then transparent objects render one at a time. This is noted already but since it's the root cause of many problems it should be clarified.
• Transparent objects do not show up on screen textures
• Some effects, like SSR or SDFGI, don't work with transparency
• Transparent object do not cast shadows (without a workaround)

These facts are currently documented in several places, across several pages. Sometimes they are duplicated, sometimes they are not duplicated and it causes problems.

These facts (and any other known limitations of transparency) should be added to the 3D rendering limitations page, as a new subsection of the existing Transparency sorting section. Existing notes on transparency limitations on other pages should stay as they are (or be slightly abridged), and also link to this new section.

URL to the documentation page (if already existing):
Existing limitations page: https://docs.godotengine.org/en/stable/tutorials/3d/3d_rendering_limitations.html#transparency-sorting
Existing notes on https://docs.godotengine.org/en/stable/tutorials/shaders/shader_reference/spatial_shader.html#light-built-ins,
https://docs.godotengine.org/en/stable/tutorials/shaders/screen-reading_shaders.html#behind-the-scenes,
https://docs.godotengine.org/en/stable/tutorials/3d/standard_material_3d.html#transparency (the note here actually lists pretty much all the problems. It should be the basis for the new section)