[scrollbar-styling] Implement dynamic changing of scrollbar-width
<rdar://problem/131580592>
Pull request: https://github.com/WebKit/WebKit/pull/30731
*** Bug 257430 has been marked as a duplicate of this bug. ***
Committed 282018@main (56109dd1e516): <https://commits.webkit.org/282018@main> Reviewed commits have been landed. Closing PR #30731 and removing active labels.
*** Bug 257425 has been marked as a duplicate of this bug. ***