Port WebHitTestResultData to the new IPC serialization format
<rdar://problem/102518135>
Pull request: https://github.com/WebKit/WebKit/pull/6637
Committed 257087@main (39afa29edb26): <https://commits.webkit.org/257087@main> Reviewed commits have been landed. Closing PR #6637 and removing active labels.
Bug 248512 – [WinCairo] REGRESSION(257087@main): assertion failed in IPC::ArgumentCoder<WebKit::WebHitTestResultData,void>::decode