Move get element functionality to a helper (#33327)

Looking around on js components I found out many checks, different expressed but with same purpose.
Some of them are trying to parse string to element, others, jQuery element to js simple nodeElement etc

With this Pr, I am trying to give a standard way to parse an element

So this pr:

* Creates `getElement` helper that tries to parse an argument to element or null
* Changes `isElement` to make  explicit checks and return Boolean 
* fixes tests deficiencies

js/tests/unit/util/index.spec.js

@@ -1,7 +1,7 @@
 import * as Util from '../../../src/util/index'
 
 /** Test helpers */
-import { getFixture, clearFixture } from '../../helpers/fixture'
+import { clearFixture, getFixture } from '../../helpers/fixture'
 
 describe('Util', () => {
   let fixtureEl
@@ -171,24 +171,58 @@ describe('Util', () => {
   })
 
   describe('isElement', () => {
-    it('should detect if the parameter is an element or not', () => {
-      fixtureEl.innerHTML = '<div></div>'
+    it('should detect if the parameter is an element or not and return Boolean', () => {
+      fixtureEl.innerHTML =
+        [
+          '<div id="foo" class="test"></div>',
+          '<div id="bar" class="test"></div>'
+        ].join('')
 
-      const el = document.querySelector('div')
+      const el = fixtureEl.querySelector('#foo')
 
-      expect(Util.isElement(el)).toEqual(el.nodeType)
-      expect(Util.isElement({})).toEqual(undefined)
+      expect(Util.isElement(el)).toEqual(true)
+      expect(Util.isElement({})).toEqual(false)
+      expect(Util.isElement(fixtureEl.querySelectorAll('.test'))).toEqual(false)
     })
 
     it('should detect jQuery element', () => {
       fixtureEl.innerHTML = '<div></div>'
 
-      const el = document.querySelector('div')
+      const el = fixtureEl.querySelector('div')
       const fakejQuery = {
-        0: el
+        0: el,
+        jquery: 'foo'
       }
 
-      expect(Util.isElement(fakejQuery)).toEqual(el.nodeType)
+      expect(Util.isElement(fakejQuery)).toEqual(true)
+    })
+  })
+
+  describe('getElement', () => {
+    it('should try to parse element', () => {
+      fixtureEl.innerHTML =
+        [
+          '<div id="foo" class="test"></div>',
+          '<div id="bar" class="test"></div>'
+        ].join('')
+
+      const el = fixtureEl.querySelector('div')
+
+      expect(Util.getElement(el)).toEqual(el)
+      expect(Util.getElement('#foo')).toEqual(el)
+      expect(Util.getElement('#fail')).toBeNull()
+      expect(Util.getElement({})).toBeNull()
+      expect(Util.getElement([])).toBeNull()
+      expect(Util.getElement()).toBeNull()
+      expect(Util.getElement(null)).toBeNull()
+      expect(Util.getElement(fixtureEl.querySelectorAll('.test'))).toBeNull()
+
+      const fakejQueryObject = {
+        0: el,
+        jquery: 'foo'
+      }
+
+      expect(Util.getElement(fakejQueryObject)).toEqual(el)
     })
   })