Improved logic for CharacterBody collision recovery depth

Allows 2D character controller to work without applying gravity when
touching the ground (also more safely in 3D), and collision detection
is more flexible with different safe margin values.

Character body motion changes in 2D and 3D:
-Recovery only for depth > min contact depth to help with collision
detection consistency (rest info could be lost if recovery was too much)
-Adaptive min contact depth (based on margin) instead of space parameter

Extra CharacterBody changes:
-2D: apply changes made in 3D for stop on slope and floor snap that help
fixing some jittering cases
-3D: fix minor inconsistencies in stop on slope and floor snap logic

servers/physics_server_2d.cpp

@@ -670,7 +670,6 @@ void PhysicsServer2D::_bind_methods() {
 	BIND_ENUM_CONSTANT(SPACE_PARAM_BODY_ANGULAR_VELOCITY_SLEEP_THRESHOLD);
 	BIND_ENUM_CONSTANT(SPACE_PARAM_BODY_TIME_TO_SLEEP);
 	BIND_ENUM_CONSTANT(SPACE_PARAM_CONSTRAINT_DEFAULT_BIAS);
-	BIND_ENUM_CONSTANT(SPACE_PARAM_TEST_MOTION_MIN_CONTACT_DEPTH);
 
 	BIND_ENUM_CONSTANT(SHAPE_WORLD_BOUNDARY);
 	BIND_ENUM_CONSTANT(SHAPE_SEPARATION_RAY);