Ensure that Gesturable interactions that use an existing gesture recognizer prime the initial state.
Summary: This was causing a bug in the contextual transition and modal transition demos because runtime.toggle(spring, inReactionTo: draggable) in Tossable wasn't disabling the spring immediately when Draggable used an already-active gesture recognizer.
Reviewed By: O4 Material Apple platform reviewers, chuga
Tags: Material Motion
Differential Revision: http://codereview.cc/D2889