Make it easier to test multiple types in IPCSerialization, and use it to test NSURL and NSData
<rdar://problem/117548102>
Pull request: https://github.com/WebKit/WebKit/pull/19601
Committed 269828@main (4ee7d142938d): <https://commits.webkit.org/269828@main> Reviewed commits have been landed. Closing PR #19601 and removing active labels.