Enable setting of collision iterations in PhysicsServer2D

This allows fine-tuning of collision iterations for more
accurate collision physics with a performance cost.

doc/classes/PhysicsServer2D.xml

@@ -1018,6 +1018,15 @@
 				Activates or deactivates the 2D physics engine.
 			</description>
 		</method>
+		<method name="set_collision_iterations">
+			<return type="void">
+			</return>
+			<argument index="0" name="iterations" type="int">
+			</argument>
+			<description>
+				Sets the amount of iterations for calculating velocities of colliding bodies. The greater the amount, the more accurate the collisions, but with a performance loss.
+			</description>
+		</method>
 		<method name="shape_get_data" qualifiers="const">
 			<return type="Variant">
 			</return>

servers/physics_2d/physics_server_2d_sw.cpp

@@ -1237,6 +1237,10 @@ void PhysicsServer2DSW::set_active(bool p_active) {
 	active = p_active;
 };
 
+void PhysicsServer2DSW::set_collision_iterations(int p_iterations) {
+	iterations = p_iterations;
+};
+
 void PhysicsServer2DSW::init() {
 	doing_sync = false;
 	last_step = 0.001;

servers/physics_2d/physics_server_2d_sw.h

@@ -288,6 +288,8 @@ public:
 	virtual void end_sync() override;
 	virtual void finish() override;
 
+	virtual void set_collision_iterations(int p_iterations) override;
+
 	virtual bool is_flushing_queries() const override { return flushing_queries; }
 
 	int get_process_info(ProcessInfo p_info) override;

servers/physics_2d/physics_server_2d_wrap_mt.h

@@ -303,6 +303,7 @@ public:
 
 	FUNC1(free, RID);
 	FUNC1(set_active, bool);
+	FUNC1(set_collision_iterations, int);
 
 	virtual void init() override;
 	virtual void step(real_t p_step) override;

servers/physics_server_2d.cpp

@@ -675,6 +675,8 @@ void PhysicsServer2D::_bind_methods() {
 
 	ClassDB::bind_method(D_METHOD("set_active", "active"), &PhysicsServer2D::set_active);
 
+	ClassDB::bind_method(D_METHOD("set_collision_iterations", "iterations"), &PhysicsServer2D::set_collision_iterations);
+
 	ClassDB::bind_method(D_METHOD("get_process_info", "process_info"), &PhysicsServer2D::get_process_info);
 
 	BIND_ENUM_CONSTANT(SPACE_PARAM_CONTACT_RECYCLE_RADIUS);

servers/physics_server_2d.h

@@ -589,6 +589,8 @@ public:
 
 	virtual bool is_flushing_queries() const = 0;
 
+	virtual void set_collision_iterations(int iterations) = 0;
+
 	enum ProcessInfo {
 		INFO_ACTIVE_OBJECTS,
 		INFO_COLLISION_PAIRS,