This adds the ability to keyframe more than one value per input (e.g. a vec2,
vec3, etc.) so that you can animate, for example, an X axis separately from a
Y axis.
Widget now supports creating keyframe and standard values, supports dragging
from sliders (not creating an undo command for each drag), and everything is
undoable.
Previously the non-keyframed value was stored as a static keyframe but this
introduced issues when an input was in a state of keyframes being enabled but
0 keyframes existing. Having a standard value makes much more sense.
itsmattkc