Fix emoji input on iOS (bustle#764)

* Fix emoji inputs.

Emoji char codes are bigger than String.fromCharCode() supports. String.fromCodePoint() has a larger range.

Fixes TryGhost/Ghost#11541.

* Add a unit test.

Co-authored-by: Garth Poitras <411908+gpoitch@users.noreply.github.com>

src/js/utils/key.js

@@ -83,7 +83,7 @@ const Key = class Key {
 
   toString() {
     if (this.isTab()) { return TAB; }
-    return String.fromCharCode(this.charCode);
+    return String.fromCodePoint(this.charCode);
   }
 
   // See https://caniuse.com/#feat=keyboardevent-key for browser support.

tests/unit/utils/key-test.js

@@ -91,3 +91,15 @@ test('uses keyCode as a fallback if key is not supported', (assert) => {
     'keyCode is used if key is not supported'
   );
 });
+
+test('properly handles UTF-16 characters', assert => {
+  let element = $('#qunit-fixture')[0];
+
+  let event = Helpers.dom.createMockEvent('keypress', element, {
+    key: '😀',
+    keyCode: 128512,
+    charCode: 128512,
+  });
+  let keyInstance = Key.fromEvent(event);
+  assert.equal('😀', keyInstance.toString(), 'emoji was not properly decoded');
+});