Make more use of smart pointers in files under Source/WebKit/Shared/.
Pull request: https://github.com/WebKit/WebKit/pull/16873
Committed 267232@main (cc21d6f48180): <https://commits.webkit.org/267232@main> Reviewed commits have been landed. Closing PR #16873 and removing active labels.
<rdar://problem/114388940>