Returns the value from the siTimeControlExtrapolationType
enum that corresponds to how a clip contributes to the animation
after the frames on which it is defined.
On the Time Control property editor, this appears on the
Extrapolation tab under After as the Type parameter. The value of
this property determines what kind of value will be considered for
the ExtrapolationAfterValue. For example, if ExtrapolationAfterType
is set to 3 ('Bounce'), then the ExtrapolationAfterValue will read
from the 'Bounces' parameter.