Make interface types a string

This is more in line with wayland and it allows us to create new
interfaces in modules without having to add anything to the type
enum. It also removes some lookups to map type_id to readable
name in debug.

pipewire-pulseaudio/src/internal.h

@@ -219,7 +219,7 @@ struct param {
 struct global {
 	struct spa_list link;
 	uint32_t id;
-	uint32_t type;
+	char *type;
 	struct pw_properties *props;
 
 	pa_context *context;