Simplify the load of icon theme icons from JavaScript code

In https://github.com/xwiki/xwiki-platform/blob/cace65ffccdac07d4a168d56cb5de6649701ed50/xwiki-platform-core/xwiki-platform-security/xwiki-platform-security-requiredrights/xwiki-platform-security-requiredrights-ui/src/main/resources/js/security/requiredrights/requiredRightsDialog.js#L75-L165 we already have a relatively comprehensive icon loader helper that could be made generally available. I'm sure it could be improved, but it actually already does more than what the code where it is used needs.

This could be extracted in the standard JS module I mentioned. But on my side I think we should keep the RequireJS loader plugin to allow RequireJS modules to easily loads their icons. This loaded plugin would call the standard JS module.