Add CookieChangeListener base class and make WebCookieCache a CookieChangeListener
Pull request: https://github.com/WebKit/WebKit/pull/16294
<rdar://problem/111903092>
Committed 266570@main (08f56b30694c): <https://commits.webkit.org/266570@main> Reviewed commits have been landed. Closing PR #16294 and removing active labels.