[Reviewed] [3D particle emitter] Fix the emission zone radius and relative particles with the 3D renderer world scale

[4ian]

Follow-up of #2277 (emission zone radius) and #2193, for the Three.js upgrade: 4ian/GDevelop#8853

The emitter is in the layer, whose Three.js scene is scaled by 1 / worldScale. So the emitter's world matrix already converts the emitter shape, and the velocities of relative particles, from pixels to Three.js world units. Converting them in the extension too divided them by the world scale twice.

Changes (3.2.0 → 3.2.1)

• Emission zone radius: no longer multiplied by inverseWorldScale. Zones were 100× too small with the upgrade.
• Start speed and gravity: converted only for particles in world space. three.quarks cancels the emitter scale on world-space velocities, so Handle the 3D renderer world scale in some extensions #2193's conversion is right there. For relative particles ("Are particles relative"), velocities are in emitter units, and they were 100× too slow. The values are kept and re-applied when the relative setting changes.
• Trail start length: no longer converted. It's a number of recorded positions ("one per frame"), not a distance: 120 became 1.2, which made trails almost invisible.
• Emitter creation: updateWorldMatrix(true, true) instead of updateMatrixWorld(true), so the parents (with the layer scale) are up to date and the very first particles get the right scale too.

Nothing changes on GDevelop versions without the world scale (inverseWorldScale is 1 there).

Testing

verifyExtension('ParticleEmitter3D') returns success.

I created an emitter in the 3D tank example (zone radius 500, spray angle 0, speed 100), rendered every frame, and measured the spawned particles in pixels on a GDevelop build with the runtime of #8853 and on the current release:

	Mode	Mean distance to the emitter	Speed
Before, with #8853	world space	3.5 px (median)	100 px/s
Before, with #8853	relative	3.5 px	1 px/s
After, with #8853	world space	341 px	100 px/s
After, with #8853	relative	343 px	100 px/s
After, current release	world space / relative	415 / 316 px	100 px/s

(The expected mean distance in a disc of radius 500 is ~333 px; differences come from the random spawn positions.)

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