Add: Add a react hook for storing instance variables

An instance variable stores the value directly and doesn't cause
re-renders if it is changed. Variables returned from this hooks are
comparable to instance variables for class components.

src/web/hooks/useInstanceVariable.js

@@ -0,0 +1,26 @@
+/* SPDX-FileCopyrightText: 2024 Greenbone AG
+ *
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+import {useRef} from 'react';
+
+/**
+ * A hook to store an instance variable for a function component.
+ *
+ * This variable is persistent during render phases and changes to the variable
+ * don't cause re-renders like useState does. It is comparable to storing a
+ * variable to this in a class component.
+ *
+ * https://reactjs.org/docs/hooks-faq.html#is-there-something-like-instance-variables
+ *
+ * @param {*} initialValue Initial value of the variable. Can be any kind of
+ *                         object. Most of the time it should be initialized
+ *                         with an empty object.
+ */
+const useInstanceVariable = initialValue => {
+  const ref = useRef(initialValue);
+  return ref.current;
+};
+
+export default useInstanceVariable;