[upstream] Bug fixes (box2d #897)

rename null joint to filter joint (less confusing)
fix for polygon collision in the speculative region
example of kinematic target
fixed cast result consistency
gate demo
more character mover testing

box2d #875
box2d #880
box2d #868

Author: ikpil

data/map01.svg

@@ -128,7 +128,7 @@ void BuildScene()
                         box = b2MakeBox(halfWidth, ratio * halfWidth);
                     }
 
-                    int category = (int)RandomIntRange(0, 2);
+                    int category = RandomIntRange(0, 2);
                     shapeDef.filter.categoryBits = (ulong)(1 << category);
                     if (category == 0)
                     {