If available, add entity id as data attribute to VBO checkbox

Created a patch for this.

Patch also works on (latest) version 4.2.4

This is causing an error when updating views_bulk_operations to version 4.2.6:
Warning: Undefined array key 24 in /var/www/html/web/modules/contrib/views_bulk_operations/src/Plugin/views/field/ViewsBulkOperationsBulkForm.php on line 695
Will update patch soon

Created patch for this

Added patch for 4.3.x

Test 2 for 4.3.x

Oh dear, wish I thought about this one earlier.. Entity ID actually is in each checkbox value. Check this line on how it's generated and this line on how it's decoded in PHP.

You can decode that bulk form key in JS as well:
https://developer.mozilla.org/en-US/docs/Web/API/Window/atob
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global...

I hope this helps.