prev() function fails when non-element nodes are present (#30117)

The `prev()` function doesn't take nodes other than elements into account. Also we could simplify things a lot using the `previousElementSibling` property. This property isn't fully supported in IE, it only works for elements, but since the `element` variable is an element, we can safely use it here.

I've also added an additional test.

I don't think we had this issue in v4, since we relied on jQuery back then.

Ref. https://developer.mozilla.org/en-US/docs/Web/API/NonDocumentTypeChildNode/nextElementSibling

js/tests/unit/dom/selector-engine.spec.js

@@ -110,6 +110,21 @@ describe('SelectorEngine', () => {
 
       expect(SelectorEngine.prev(btn, '.test')).toEqual([divTest])
     })
+
+    it('should return previous element with comments or text nodes between', () => {
+      fixtureEl.innerHTML = [
+        '<div class="test"></div>',
+        '<div class="test"></div>',
+        '<!-- Comment-->',
+        'Text',
+        '<button class="btn"></button>'
+      ].join('')
+
+      const btn = fixtureEl.querySelector('.btn')
+      const divTest = fixtureEl.querySelectorAll('.test')[1]
+
+      expect(SelectorEngine.prev(btn, '.test')).toEqual([divTest])
+    })
   })
 })