Vulkan: GPUParticles2D attractors not implemented yet (unlike in GPUParticles3D)

[Calinou]

Related to #60910.

Godot version

4.0.alpha7

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 510.60.02)

Issue description

GPUParticles2D attractors aren't implemented yet (unlike in GPUParticles3D):

Steps to reproduce

• Look for GPUParticles2D attractor shape nodes in the Create New Node dialog.

Minimal reproduction project

N/A

[cosparks]

I've been investigating this issue and am wondering whether or not a 2D attractor node should extend LightOccluder2D, or if this warrants a new branch of nodes which aligns with how GPUParticlesCollision3D and GPUParticlesAttractor3D work -- ie. we could have GPUParticlesCollision2D and GPUParticlesAttractor2D.

I am leaning toward the former but honestly the difference in naming between 2d and 3d gpu collision nodes seems a bit strange, so was wondering if there is interest in creating a specialized GPUParticlesCollision2D node.