Use generics for typing nodeListForEach

This allows to forward the type of the `NodeListOf` it iterates on to the parameters of the callback.
In turn this should allow to drop quite a few `instanceof` checks when using the function by properly typing the `NodeList` we give it.

Interesting links:
- [The `@template` JSDoc tag](https://www.typescriptlang.org/docs/handbook/jsdoc-supported-types.html#template)
- [How to constrain the generic type](https://stackoverflow.com/a/54631901)

src/govuk/common/index.mjs

@@ -13,8 +13,9 @@
  * This seems to fail in IE8, requires more investigation.
  * See: https://github.com/imagitama/nodelist-foreach-polyfill
  *
- * @param {NodeListOf<Element>} nodes - NodeList from querySelectorAll()
- * @param {nodeListIterator} callback - Callback function to run for each node
+ * @template {Node} ElementType
+ * @param {NodeListOf<ElementType>} nodes - NodeList from querySelectorAll()
+ * @param {nodeListIterator<ElementType>} callback - Callback function to run for each node
  * @returns {void}
  */
 export function nodeListForEach (nodes, callback) {
@@ -161,9 +162,10 @@ export function extractConfigByNamespace (configObject, namespace) {
 }
 
 /**
+ * @template {Node} ElementType
  * @callback nodeListIterator
- * @param {Element} value - The current node being iterated on
+ * @param {ElementType} value - The current node being iterated on
  * @param {number} index - The current index in the iteration
- * @param {NodeListOf<Element>} nodes - NodeList from querySelectorAll()
+ * @param {NodeListOf<ElementType>} nodes - NodeList from querySelectorAll()
  * @returns {void}
  */