Add: Add jsdoc comments for string functions

Document the string functions.

Author: bjoernricks

src/gmp/utils/string.js

@@ -5,9 +5,22 @@
 
 import {isDefined, isString} from './identity';
 
+/**
+ * Capitalizes the first letter of a given string.
+ *
+ * @param {string} string - The string to capitalize.
+ * @returns {string} The string with the first letter capitalized.
+ */
 export const capitalizeFirstLetter = string =>
   string.charAt(0).toUpperCase() + string.slice(1);
 
+/**
+ * Shortens a given text to a specified length, appending '...' if the text exceeds the length.
+ *
+ * @param {string} [text=''] - The text to be shortened.
+ * @param {number} [length=60] - The maximum length of the shortened text.
+ * @returns {string} - The shortened text.
+ */
 export const shorten = (text = '', length = 60) => {
   if (!isString(text)) {
     text = `${text}`;
@@ -46,4 +59,12 @@ export const split = (string, separator, limit) => {
   return splits;
 };
 
+/**
+ * Checks if a given string is empty.
+ *
+ * A string is considered empty if it is either undefined or has a length of 0.
+ *
+ * @param {string} string - The string to check.
+ * @returns {boolean} - Returns true if the string is empty, otherwise false.
+ */
 export const isEmpty = string => !isDefined(string) || string.length === 0;