dialog: add title setter to API

src/lib/Dialog.svelte

@@ -23,6 +23,11 @@
 		unfreeze: () => void;
 		/** if the default controls are used, returns true if the dialog is frozen */
 		isFrozen: () => boolean;
+		/**
+		 * title sets the dialog title. WARNING: Title is NOT bindable and
+		 * changes made via this API will NOT propagate to consuming components.
+		 */
+		title: (title: string) => void;
 	}
 
 	/**
@@ -107,7 +112,8 @@
 		isLoading: () => loading,
 		freeze: () => (frozen = true),
 		unfreeze: () => (frozen = false),
-		isFrozen: () => frozen
+		isFrozen: () => frozen,
+		title: (newTitle) => (title = newTitle)
 	};
 </script>