Allow trail particles to be parented to their spawner

[BMagnu]

This one's a little more complicated.
Prior to this, a particle that's a trail of another particle with both having local to parent set to true would transitively inherit the parent trail's parent object.
As evident, this also runs into naming ambiguity, so this PR cleans this up.
Parent, as in the thing that spawned a particle, is (and really was already) called "Host". A spawner tracks its host, gets its position and other data for curves.
Parent, as in the thing that a particle uses as frame of reference for local coordinates, is now called an Attachment. Attachments provide a frame of reference, and functions to convert local and global coordinates, no matter what they actually are (currently can be either nothing, an object, or a particle).
In order to get around the prior behavior of transitive attachments by default, this adds a table option to selectively disable transitivity. If that is set to true, a child particle will not inherit the underlying object attachment, but the particle as an attachment.

This allows more complex particle trail chains, some of which have been shown to be necessary for certain type of explosion effects actually encountered during modding.

It also cleans up the code by moving a fair bit of ad-hoc checks and coordinate space conversions into their own dedicated functions

The added indirection through the variant does cost some performance, but IMO it stays in an acceptable cost frame.
The following is a testing mission with 300k particles and nothing else: