Fix radial inwards velocity clamping incorrectly (regression from #83488)

[QbieShay]

When i changed the particle code to avoid division by zero, i didn't notice i left out a part in rdial velocity, which now causes radial velocity around the center to just be a fixed speed. This correctly fixes it.

Bugsquad edit:

• Regression fix after Fixed multiple particle issues: division by zero, color ramp override, scale dependent on amount ratio #83488

[QbieShay]

Alright so!

This fix is the correct fix, because the variables that are named "displacement" are actually velocities. They used to be raw displacement, but in order to fix some division by zero i did a rework of the functions to instead calculate velocities, but unfortunately i didn't rename the parameters/functions to correctly represent it.

Doing a bunch of renames at this stage of RC is not ideal, so what I suggest it's the following:

1. merge this fix (otherwise inwards radial velocity is unusable)
2. for 4.3, fix the naming ( I opened and self assigned an issue for it Particle Shader calls velocities displacement #85310 )

[clayjohn]

Thank you for the explanation. Indeed this is very confusing because the naming consistently refers to a displacement, but it is calculating a velocity.

On review I can see that all the other components that contribute to radial_displacement (and controlled_displacement) are velocities. So it makes sense to convert this value into a velocity as well.

[akien-mga]

Thanks!