This is a preparation for https://bugs.webkit.org/show_bug.cgi?id=256153. First we need to handle disclosure-closed as one of the special complex systems, such that we can consider RTL context when calculating its text value. Later on we should also consider writing-mode but that should come as a separated bug.
<rdar://problem/128708419>
Pull request: https://github.com/WebKit/WebKit/pull/29089