popGestureEnabled property
Whether a pop gesture can be started by the user.
Returns true if the user can edge-swipe to a previous route.
Returns false once isPopGestureInProgress is true, but
isPopGestureInProgress can only become true if popGestureEnabled was
true first.
This should only be used between frames, not during build.
Implementation
@override
bool get popGestureEnabled => _isPopGestureEnabled(this);