Make allowing site-wide styles on restricted special pages a config option

This mostly reverts commit 614d7e5c274d927f99bfc52ac3a1e6c7e5902408.

Many wikis use MediaWiki:Common.css and associated pages to create a
custom "theme" for their wiki, which would no longer load on login
or preference pages, creating an inconsistent UI.

This re-adds the difference in module origin for different types
(styles, scripts, etc.), and now OutputPage::disallowUserJs()
checks the value of the "AllowSiteCSSOnRestrictedPages" config setting
to determine whether to allow site-wide CSS styles or not.

By default this feature is disabled to be secure by default.

Bug: 71621
Change-Id: I1bf4dd1845b6952c3985e179fbea48181ffb8907