Fix NSGraphicsContext deprecated methods and inner-pointer lifetime issues.
Created attachment 398577 [details] Patch v1
The CGContext methods were added in Mac OS X 10.10, and the GraphicsPort methods were deprecated in macOS 10.14.
Committed r261210: <https://trac.webkit.org/changeset/261210> All reviewed patches have been landed. Closing bug and clearing flags on attachment 398577 [details].
<rdar://problem/62915521>