Changes to 2D physics engine

-=-=-=-=-=-=-=-=-=-=-=-=-=-=

-Removed "density" property
-Added instead more flexible "angular damp" and "linear damp"
-Added ability to override angular and linear damp in rigidbody
-Added gravity scale option rigidbody

Test well and iron out bugs, when it works the same will be moved to 3D

servers/physics_2d_server.h

@@ -43,7 +43,8 @@ protected:
 public:
 
 	virtual Vector2 get_total_gravity() const=0; // get gravity vector working on this body space/area
-	virtual float get_total_density() const=0; // get density of this body space/area
+	virtual float get_total_linear_damp() const=0; // get density of this body space/area
+	virtual float get_total_angular_damp() const=0; // get density of this body space/area
 
 	virtual float get_inverse_mass() const=0; // get the mass
 	virtual real_t get_inverse_inertia() const=0; // get density of this body space
@@ -277,7 +278,6 @@ public:
 		SPACE_PARAM_BODY_LINEAR_VELOCITY_SLEEP_TRESHOLD,
 		SPACE_PARAM_BODY_ANGULAR_VELOCITY_SLEEP_TRESHOLD,
 		SPACE_PARAM_BODY_TIME_TO_SLEEP,
-		SPACE_PARAM_BODY_ANGULAR_VELOCITY_DAMP_RATIO,
 		SPACE_PARAM_CONSTRAINT_DEFAULT_BIAS,
 	};
 
@@ -301,7 +301,8 @@ public:
 		AREA_PARAM_GRAVITY_VECTOR,
 		AREA_PARAM_GRAVITY_IS_POINT,
 		AREA_PARAM_GRAVITY_POINT_ATTENUATION,
-		AREA_PARAM_DENSITY,
+		AREA_PARAM_LINEAR_DAMP,
+		AREA_PARAM_ANGULAR_DAMP,
 		AREA_PARAM_PRIORITY
 	};
 
@@ -401,6 +402,9 @@ public:
 		BODY_PARAM_BOUNCE,
 		BODY_PARAM_FRICTION,
 		BODY_PARAM_MASS, ///< unused for static, always infinite
+		BODY_PARAM_GRAVITY_SCALE,
+		BODY_PARAM_LINEAR_DAMP,
+		BODY_PARAM_ANGULAR_DAMP,
 		BODY_PARAM_MAX,
 	};
 
@@ -414,7 +418,7 @@ public:
 		BODY_STATE_LINEAR_VELOCITY,
 		BODY_STATE_ANGULAR_VELOCITY,
 		BODY_STATE_SLEEPING,
-		BODY_STATE_CAN_SLEEP
+		BODY_STATE_CAN_SLEEP,
 	};
 
 	virtual void body_set_state(RID p_body, BodyState p_state, const Variant& p_variant)=0;