Bug 1756488 - trigger update of react state for bug filer after log content got copied into it with button

The button to transfer selected text from the log viewer into the bug filer in a
different tab got added in bug bug 1745936 but didn't trigger React's `onChange`
event.

ui/logviewer/App.jsx

@@ -225,6 +225,10 @@ class App extends React.PureComponent {
       descriptionField.value.substring(endPos, descriptionField.value.length);
     descriptionField.selectionStart = startPos + selectedLogText.length;
     descriptionField.selectionEnd = startPos + selectedLogText.length;
+
+    const event = document.createEvent('HTMLEvents');
+    event.initEvent('change', true, true);
+    descriptionField.dispatchEvent(event);
   };
 
   collapseJobDetails = () => {