jack: Pass custom flags as port.extra info

Make a port.extra property that contains API specific extra port
information that is passed in the global object properties.
Use this to pass the custom jack flags for a port. Carla uses this
to mark CV ports.

src/pipewire/impl-port.c

@@ -837,6 +837,7 @@ int pw_impl_port_register(struct pw_impl_port *port,
 		PW_KEY_PORT_TERMINAL,
 		PW_KEY_PORT_CONTROL,
 		PW_KEY_PORT_ALIAS,
+		PW_KEY_PORT_EXTRA,
 		NULL
 	};
 

src/pipewire/keys.h

@@ -157,6 +157,8 @@ extern "C" {
 #define PW_KEY_PORT_CONTROL		"port.control"		/**< if this port is a control port */
 #define PW_KEY_PORT_MONITOR		"port.monitor"		/**< if this port is a monitor port */
 #define PW_KEY_PORT_CACHE_PARAMS	"port.cache-params"	/**< cache the node port params */
+#define PW_KEY_PORT_EXTRA		"port.extra"		/**< api specific extra port info, API name
+								  *  should be prefixed. "jack:flags:56" */
 
 /** link properties */
 #define PW_KEY_LINK_ID			"link.id"		/**< a link id */