For the time being we don't support writing a description for those, preferring
having all details in the method's description.
Using self-closing tags saves half the lines, and prevents contributors from
thinking that they should write the argument or return documentation there.
(cherry picked from commit 7adf4cc9b5)
We already removed it from the online docs with #35132.
Currently it can only be "Built-In Types" (Variant types) or "Core"
(everything else), which is of limited use.
We might also want to consider dropping it from `ClassDB` altogether
in Godot 4.0.
- Add some missing descriptions.
- Add links to tutorials for ARVR and AnimationTree.
- Style fixes.
- Engine changes:
* Make `AnimationNodeTransition.input_<number>` properties internal
so that they don't appear in the docs. They still appear in the
inspector based on the actual number of inputs requested.
* Drop unimplemented `CPUParticles.flatness`. It's only used for 3D
particles in `ParticlesMaterial`, and thus only relevant for
`CPUParticles3D`.
