ThreadSafeObjectHeap should be part of IPC - It is used to manage references of IPC objects - IPC code can be tested
<rdar://problem/110165802>
Pull request: https://github.com/WebKit/WebKit/pull/14625
Committed 264861@main (6494a227e779): <https://commits.webkit.org/264861@main> Reviewed commits have been landed. Closing PR #14625 and removing active labels.