Among all the lines moved around, the general idea is quite simple.
Actually, there are two ideas implemented there.
First one, is when object itself is tagged for update, we tag its
point cache component for evaluation, which makes it so point cache
is properly reset. We do it implicitly because otherwise we'll need
to go everywhere and add explicit tag in almost all the properties.
Second thing is, we link all collider and force fields to a point
cache component using special type of link. This type of link only
allows flush if change is caused by a user update. This way reset
does not happen when change is caused due to animation, but will
properly happen when user causes indirect change to the objects
which are part of physics simulation.
To find all effectors in the scene, we need to loop over all objects.
Doing this during depsgraph evaluation caused crashes because not all
objects are guaranteed to be evaluated yet.
To fix this, we now cache the relations as part of the dependency graph
build. As a bonus this also makes evaluation faster for big scenes,
since looping over all objects for each particle system is slow.
Fixes T55156.
