Mark common helpers as deprecated

package/govuk-esm/common/closest-attribute-value.mjs

@@ -3,6 +3,7 @@ import '../vendor/polyfills/Element/prototype/closest.mjs'
 /**
  * Returns the value of the given attribute closest to the given element (including itself)
  *
+ * @deprecated Will be made private in v5.0
  * @param {HTMLElement} $element - The element to start walking the DOM tree up
  * @param {string} attributeName - The name of the attribute
  * @returns {string | undefined} Attribute value

package/govuk-esm/common/index.mjs

@@ -13,6 +13,7 @@
  * This seems to fail in IE8, requires more investigation.
  * See: /~https://github.com/imagitama/nodelist-foreach-polyfill
  *
+ * @deprecated Will be made private in v5.0
  * @param {NodeListOf<Element>} nodes - NodeList from querySelectorAll()
  * @param {nodeListIterator} callback - Callback function to run for each node
  * @returns {void}
@@ -31,6 +32,7 @@ export function nodeListForEach (nodes, callback) {
  * without them conflicting with each other.
  * https://stackoverflow.com/a/8809472
  *
+ * @deprecated Will be made private in v5.0
  * @returns {string} Unique ID
  */
 export function generateUniqueID () {
@@ -52,6 +54,7 @@ export function generateUniqueID () {
  * (e.g. {'i18n.showSection': 'Show section'}) and combines them together, with
  * greatest priority on the LAST item passed in.
  *
+ * @deprecated Will be made private in v5.0
  * @returns {Object<string, unknown>} A flattened object of key-value pairs.
  */
 export function mergeConfigs (/* configObject1, configObject2, ...configObjects */) {
@@ -123,6 +126,7 @@ export function mergeConfigs (/* configObject1, configObject2, ...configObjects
  * Extracts keys starting with a particular namespace from a flattened config
  * object, removing the namespace in the process.
  *
+ * @deprecated Will be made private in v5.0
  * @param {Object<string, unknown>} configObject - The object to extract key-value pairs from.
  * @param {string} namespace - The namespace to filter keys with.
  * @returns {Object<string, unknown>} Flattened object with dot-separated key namespace removed

package/govuk-esm/common/normalise-dataset.mjs

@@ -14,6 +14,7 @@ import '../vendor/polyfills/String/prototype/trim.mjs'
  * Designed to be used to convert config passed via data attributes (which are
  * always strings) into something sensible.
  *
+ * @deprecated Will be made private in v5.0
  * @param {string} value - The value to normalise
  * @returns {string | boolean | number | undefined} Normalised data
  */
@@ -46,6 +47,7 @@ export function normaliseString (value) {
  *
  * Loop over an object and normalise each value using normaliseData function
  *
+ * @deprecated Will be made private in v5.0
  * @param {DOMStringMap} dataset - HTML element dataset
  * @returns {Object<string, unknown>} Normalised dataset
  */