As a follow up to https://trac.webkit.org/r277013, replace the remaining raw pointers
of elements in SVGDocumentExtensions and SVGElementRareData with WeakHashMap and WeakPtr.
Created attachment 427862 [details]
Committed r277078 (237381@main): <https://commits.webkit.org/237381@main>
All reviewed patches have been landed. Closing bug and clearing flags on attachment 427862 [details].