add get_camera_rid method

doc/classes/Camera.xml

@@ -39,6 +39,13 @@
 			<description>
 			</description>
 		</method>
+		<method name="get_camera_rid" qualifiers="const">
+			<return type="RID">
+			</return>
+			<description>
+				Returns the camera's RID from the [VisualServer].
+			</description>
+		</method>
 		<method name="is_position_behind" qualifiers="const">
 			<return type="bool">
 			</return>

scene/3d/camera.cpp

@@ -524,6 +524,7 @@ void Camera::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_doppler_tracking", "mode"), &Camera::set_doppler_tracking);
 	ClassDB::bind_method(D_METHOD("get_doppler_tracking"), &Camera::get_doppler_tracking);
 	ClassDB::bind_method(D_METHOD("get_frustum"), &Camera::get_frustum);
+	ClassDB::bind_method(D_METHOD("get_camera_rid"), &Camera::get_camera);
 
 	ClassDB::bind_method(D_METHOD("set_cull_mask_bit", "layer", "enable"), &Camera::set_cull_mask_bit);
 	ClassDB::bind_method(D_METHOD("get_cull_mask_bit", "layer"), &Camera::get_cull_mask_bit);