After discussing this with Reduz this seemed like the best way to
fix#7354. This will make composite values that contain NaN in the same
places as well as the same other values compare as the same.
Additionally non-composite values now also compare equal if they are
both NaN. This breaks IEEE specifications but this is probably what most
users expect. There is a GDScript function check for NaN if the user
needs this information.
This fixes#7354 and probably also fixes#6947
adcc211feb