add WKNavigationAction._hasOpener SPI so that the client can know the opener policy when creating a new popup or doing a navigation in that popup.
<rdar://101651907>
Pull request: https://github.com/WebKit/WebKit/pull/8778
Committed 259085@main (08b7e0857290): <https://commits.webkit.org/259085@main> Reviewed commits have been landed. Closing PR #8778 and removing active labels.