Property that returns true if the reference is valid, false otherwise.
This property does not take into account if the component is enabled or not.
This property is intended to indicate whether it is safe to read or write this reference's value.
It is not safe to use this value as a synonym for "does the target entity have component T?".
For zero-size "tag" components (which have no addressable value in chunk memory), IsValid will always
return false, even if the component is present. It is safer to use existing HasComponent features to test
for component presence.