Change bookmarkCounter to find multiple selectors (#3351)

This commit will change the bookmarkCounter function to look for
multiple selectors instead of one.  This way if we want to put the
bookmark counter elsewhere it will also be dynamic.

Ref:
- #3350

Author: kirkkwang

app/javascript/blacklight/checkbox_submit.js

@@ -37,7 +37,9 @@ export default class CheckboxSubmit {
       this.labelTarget.removeAttribute('disabled')
       this.checkboxTarget.removeAttribute('disabled')
       this.updateStateFor(!this.checked)
-      if (this.bookmarkCounter()) this.bookmarkCounter().innerHTML = json.bookmarks.count
+      this.bookmarksCounter().forEach(counter => {
+        counter.innerHTML = json.bookmarks.count;
+      });
     }).catch((error) => {
       this.handleError(error)
     })
@@ -63,8 +65,8 @@ export default class CheckboxSubmit {
     return this.form.querySelector('[data-checkboxsubmit-target="span"]')
   }
 
-  bookmarkCounter() {
-    return document.querySelector('[data-role="bookmark-counter"]')
+  bookmarksCounter() {
+    return document.querySelectorAll('[data-role="bookmark-counter"]')
   }
 
   handleError() {