Support shadow-piercing combinator >>> in trusted-click-element

Related issue:
uBlockOrigin/uBlock-issues#2971

Example usage:

...##+js(trusted-trusted-click-element, #cmpwrapper >>> .cmpboxbtnyes)

The substring before ` >>> ` must select an element with a non-null
shadow root, in which case the substring after ` >>> ` will be used
to find the element in the targeted shadow root. ` >>> ` can be used
recursively when multiple shadow root must be pierced.

assets/resources/scriptlets.js

@@ -4077,10 +4077,21 @@ function trustedClickElement(
  ? ((...args) => { safe.uboLog(...args); })
  : (( ) => { });
 
+ const querySelectorEx = (selector, context = document) => {
+ const pos = selector.indexOf(' >>> ');
+ if ( pos === -1 ) { return context.querySelector(selector); }
+ const outside = selector.slice(0, pos).trim();
+ const inside = selector.slice(pos + 5).trim();
+ const elem = context.querySelector(outside);
+ if ( elem === null ) { return null; }
+ const shadowRoot = elem.shadowRoot;
+ return shadowRoot && querySelectorEx(inside, shadowRoot);
+ };
+
  const selectorList = selectors.split(/\s*,\s*/)
  .filter(s => {
  try {
- void document.querySelector(s);
+ void querySelectorEx(s);
  } catch(_) {
  return false;
  }
@@ -4154,7 +4165,7 @@ function trustedClickElement(
  if ( Date.now() < tnext ) { return next(); }
  const selector = selectorList.shift();
  if ( selector === undefined ) { return terminate(); }
- const elem = document.querySelector(selector);
+ const elem = querySelectorEx(selector);
  if ( elem === null ) {
  selectorList.unshift(selector);
  return next(true);