Official WebKit no longer supports Mac 10.14. However, since
this system is still very much in use, we want to be able to
keep it running for a while.
This patch adds a new browser that we would compile and maintain
specifically for Mac 10.14: `deprecated-webkit-mac-10.14`. This
browser is a clone of Webkit r1443 that is the last known revision
to compile on Mac 10.14.
As we move on, we're free to modify this browser however we want,
backporting important patches.
References #5833
