Add "Hide on Contact" collision mode to ParticlesMaterial

This can be used to make particles disappear when colliding, rather
than bouncing around or sticking to surfaces.

This is useful for rain particles which should not be able to go
through floors/ceilings, but shouldn't stick to surfaces either.

doc/classes/GPUParticlesCollisionSDF3D.xml

@@ -8,7 +8,7 @@
 		Signed distance fields (SDF) allow for efficiently representing approximate collision shapes for convex and concave objects of any shape. This is more flexible than [GPUParticlesCollisionHeightField3D], but it requires a baking step.
 		[b]Baking:[/b] The signed distance field texture can be baked by selecting the [GPUParticlesCollisionSDF3D] node in the editor, then clicking [b]Bake SDF[/b] at the top of the 3D viewport. Any [i]visible[/i] [MeshInstance3D]s touching the [member extents] will be taken into account for baking, regardless of their [member GeometryInstance3D.gi_mode].
 		[b]Note:[/b] Baking a [GPUParticlesCollisionSDF3D]'s [member texture] is only possible within the editor, as there is no bake method exposed for use in exported projects. However, it's still possible to load pre-baked [Texture3D]s into its [member texture] property in an exported project.
-		[b]Note:[/b] [member ParticlesMaterial.collision_enabled] must be [code]true[/code] on the [GPUParticles3D]'s process material for collision to work.
+		[b]Note:[/b] [member ParticlesMaterial.collision_mode] must be [constant ParticlesMaterial.COLLISION_RIGID] or [constant ParticlesMaterial.COLLISION_HIDE_ON_CONTACT] on the [GPUParticles3D]'s process material for collision to work.
 		[b]Note:[/b] Particle collision only affects [GPUParticles3D], not [CPUParticles3D].
 	</description>
 	<tutorials>