animation: Split spring setup out of weston_view_animation_run()

animation: Split spring setup out of weston_view_animation_run()

All the animations override at least one parameter of the spring that
is set during the creation of the animation. Some need to do the whole
setup again.

This patch changes the initialization of a view animation to a three
step process. First, the animation is created. Then the caller sets up
the spring and calls weston_view_animation_run() to apply the effect of
the animation for the first animation frame.