Blender Git Loki

Particles: change default name to "ParticleSystem"

Since {rB7a6b46aac56b}, particle systems were named "ParticleSettings"
by default, same as particle settings themselves. These are not the same
thing and their names should reflect that.

Issue came up in T86366.

Now name them "ParticleSystem" by default, name uniqueness is preserved
for both system and settings.

Maniphest Tasks: T86366

Differential Revision: https://developer.blender.org/D10641