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.
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`.
Setters and getters have been hidden from the documentation when the matching
properties have been exposed, but some of them are parametric and require the
name or index of a given parameter to be used. So they need to be properly
documented with the type and name of the arguments they take.
For example, CPUParticles' `set_param(Parameter param, float value)`.
