Weapon dot-to-target input

[Kestrellius]

Adds a weapon lifetime input that consists of the dot product between the vector that points toward the current target and the weapon's forward vector.

[wookieejedi]

Not sure how this could happen, but if homing_object is valid but IS_VEC_NULL(&wp.homing_pos) is true, the inner if body is skipped, target_pos is never assigned, and the function eventually hits vm_vec_sub with bad data. Could fix this by adding an else return 0.f, IE

     } else {
            return 0.f;
        }

[wookieejedi]

Should dir be normalized? I think vm_vec_dot on an unnormalized `dir gives a distance-scaled projection, which seems like that isn't the intent? Normalizing before the dot would fix this I reckon...IE

vm_vec_normalize(&dir);
return vm_vec_dot(&dir, &wep_objp->orient.vec.fvec);
``

[wookieejedi]

PR description says dot product between the vector that points toward the current target and the weapon's forward vector. Just want to check, are these in the right order? I think dir = weapon - target points away from the target not towards it (so switching to target_pos - wep_objp->pos` would face torwards) but perhaps someone with better dot math can chime in. @Baezon perhaps :D