www/webkit2-gtk: update to 2.46.5

Changelog: https://github.com/WebKit/WebKit/blob/webkitgtk-2.46.5/Source/WebKit/gtk/NEWS

Now consolidated into one port with flavours since the codebase is
the same, just linked with different libraries resulting in different
SONAMEs and APIs. SONAMEs/flavours:

* GTK3 + libsoup = libwebkit2gtk-4.0 (40)
* GTK3 + libsoup3 = libwebkit2gtk-4.1 (41)
* GTK4 + libsoup3 = libwebkitgtk-6.0 (60)

Despite upstream's recommendation to use clang for better skia
optimisation, this port now USE_GCC due to extensive std::pair copy
constructor use that is not trivial to continue patching to stay
working with our libc++ version 1 ABI. See review D35327 for some
details.

Reported by: eduardo
PR: 275914
Differential Revision: https://reviews.freebsd.org/D45878