Remove jQuery from the Unicode escape button (#29369)

- Switched to plain JavaScript
- Tested the Unicode escape button functionality and it works as before

# Demo using JavaScript without jQuery

![action](https://github.com/go-gitea/gitea/assets/20454870/664f0ced-876b-4cb7-a668-bd62169fc843)

---------

Signed-off-by: Yarden Shoham <[email protected]>
Co-authored-by: wxiaoguang <[email protected]>

web_src/js/utils/dom.js

@@ -51,6 +51,10 @@ export function isElemHidden(el) {
   return res[0];
 }
 
+export function queryElemSiblings(el, selector) {
+  return Array.from(el.parentNode.children).filter((child) => child !== el && child.matches(selector));
+}
+
 export function onDomReady(cb) {
   if (document.readyState === 'loading') {
     document.addEventListener('DOMContentLoaded', cb);