Should be able to register wiki-level JSX with wiki-level admin right (not PR)

Other permissions such as UI Extension and Macro are allowed to be registered for a single wiki but Skin Extensions cannot be registered at wiki level without programming rights.

Known workaround:
Create a UI Extension which hooks org.xwiki.platform.template.header.after which is called every page load and in the content of that extension put

{{velocity}}$xwiki.jsx.use('Whatever.JsExtension'){{/velocity}}

This should be allowed by default.