Add 4 new browser snippets

triggerEvent - trigger an event on an element, insertAfter & insertBefore - parse and insert HTML after or before an element respectively, elementContains - checks if an element contains another element

snippets/insertBefore.md

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+### insertBefore
+
+Inserts an HTML string before the start of the specified element.
+
+Use `el.insertAdjacentHTML()` with a position of `'beforebegin'` to parse `htmlString` and insert it before the start of `el`.
+
+```js
+const insertBefore = (el, htmlString) => el.insertAdjacentHTML('beforebegin', htmlString);
+```
+
+```js
+insertBefore(document.getElementById('myId'),'<p>before</p>'); // <p>before</p> <div id="myId">...</div>
+```